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Message-ID: <CAMJBoFPiqQ4xS0RJjEN11uCVr=mVDeK_ROKkYkY5oGCecyNu8A@mail.gmail.com>
Date: Wed, 23 Sep 2015 10:07:44 +0200
From: Vitaly Wool <vitalywool@...il.com>
To: Dan Streetman <ddstreet@...e.org>
Cc: Seth Jennings <sjennings@...iantweb.net>,
Andrew Morton <akpm@...ux-foundation.org>,
Minchan Kim <minchan@...nel.org>,
Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
linux-kernel <linux-kernel@...r.kernel.org>,
Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH v2] zbud: allow up to PAGE_SIZE allocations
On Tue, Sep 22, 2015 at 11:49 PM, Dan Streetman <ddstreet@...e.org> wrote:
> On Tue, Sep 22, 2015 at 8:17 AM, Vitaly Wool <vitalywool@...il.com> wrote:
>> Currently zbud is only capable of allocating not more than
>> PAGE_SIZE - ZHDR_SIZE_ALIGNED - CHUNK_SIZE. This is okay as
>> long as only zswap is using it, but other users of zbud may
>> (and likely will) want to allocate up to PAGE_SIZE. This patch
>> addresses that by skipping the creation of zbud internal
>> structure in the beginning of an allocated page (such pages are
>> then called 'headless').
>>
>> As a zbud page is no longer guaranteed to contain zbud header, the
>> following changes had to be applied throughout the code:
>> * page->lru to be used for zbud page lists
>> * page->private to hold 'under_reclaim' flag
>>
>> page->private will also be used to indicate if this page contains
>> a zbud header in the beginning or not ('headless' flag).
>>
>> Signed-off-by: Vitaly Wool <vitalywool@...il.com>
>> ---
>> mm/zbud.c | 194 +++++++++++++++++++++++++++++++++++++++++---------------------
>> 1 file changed, 128 insertions(+), 66 deletions(-)
>>
>> diff --git a/mm/zbud.c b/mm/zbud.c
>> index fa48bcdf..7b51eb6 100644
>> --- a/mm/zbud.c
>> +++ b/mm/zbud.c
>> @@ -105,18 +105,25 @@ struct zbud_pool {
>>
>> /*
>> * struct zbud_header - zbud page metadata occupying the first chunk of each
>> - * zbud page.
>> + * zbud page, except for HEADLESS pages
>
> hmm, personally I like "FULL" better than HEADLESS...it's only
> headless because it's a full page.
Yep, but OTOH, a page with two buddies is also full, so I just wanted
to avoid ambiguity here. I have no personal naming preference TBO. :)
>> * @buddy: links the zbud page into the unbuddied/buddied lists in the pool
>> - * @lru: links the zbud page into the lru list in the pool
>> * @first_chunks: the size of the first buddy in chunks, 0 if free
>> * @last_chunks: the size of the last buddy in chunks, 0 if free
>> */
>> struct zbud_header {
>> struct list_head buddy;
>> - struct list_head lru;
>> unsigned int first_chunks;
>> unsigned int last_chunks;
>> - bool under_reclaim;
>> +};
>> +
>> +/*
>> + * struct zbud_page_priv - zbud flags to be stored in page->private
>> + * @under_reclaim: if a zbud page is under reclaim
>> + * @headless: indicates a page where zbud header didn't fit
>> + */
>> +struct zbud_page_priv {
>> + bool under_reclaim:1;
>> + bool headless:1;
>> };
>
> Hmm, this is just my personal opinion, but I'm not a fan of casting
> ->private as a struct, if we're only using it as a bitmap. I'd
> suggest just defining bits as an enum (like page flags), e.g.
>
> enum zbud_flags {
> ZBUD_UNDER_RECLAIM,
> ZBUD_FULL_PAGE,
> };
Agreed, will rework that.
> or some names similar to that. then it can be checked with a simple
> test_bit() call, and set_bit()/clear_bit().
>
> alternately, there are the already-existing PG_private and
> PG_private_2 bits in the page flags...but unless we need ->private for
> something else, it probably makes more sense to just use it instead of
> the PG_private flags.
IIRC I used PG_private in my first patch but the thing also is, it's
safer to have under_reclaim flag in struct page, too, so page->private
seems to be a better fit.
>>
>> /*****************
>> @@ -221,6 +228,7 @@ MODULE_ALIAS("zpool-zbud");
>> *****************/
>> /* Just to make the code easier to read */
>> enum buddy {
>> + HEADLESS,
>> FIRST,
>> LAST
>> };
>> @@ -237,12 +245,15 @@ static int size_to_chunks(size_t size)
>> /* Initializes the zbud header of a newly allocated zbud page */
>> static struct zbud_header *init_zbud_page(struct page *page)
>> {
>> + struct zbud_page_priv *ppriv = (struct zbud_page_priv *)page->private;
>> struct zbud_header *zhdr = page_address(page);
>> +
>> + INIT_LIST_HEAD(&page->lru);
>> + ppriv->under_reclaim = 0;
>
> don't forget to initialize the headless/full bit too. (I'll mention
> that the page allocation code does clear ->private before handing it
> to us, so it should already be 0. but let's not rely on that)
>
>> +
>> zhdr->first_chunks = 0;
>> zhdr->last_chunks = 0;
>> INIT_LIST_HEAD(&zhdr->buddy);
>> - INIT_LIST_HEAD(&zhdr->lru);
>> - zhdr->under_reclaim = 0;
>> return zhdr;
>> }
>>
>> @@ -267,11 +278,22 @@ static unsigned long encode_handle(struct zbud_header *zhdr, enum buddy bud)
>> * over the zbud header in the first chunk.
>> */
>> handle = (unsigned long)zhdr;
>> - if (bud == FIRST)
>> + switch (bud) {
>> + case FIRST:
>> /* skip over zbud header */
>> handle += ZHDR_SIZE_ALIGNED;
>> - else /* bud == LAST */
>> + break;
>> + case LAST:
>> handle += PAGE_SIZE - (zhdr->last_chunks << CHUNK_SHIFT);
>> + break;
>> + case HEADLESS:
>> + break;
>> + default:
>> + /* this should never happen */
>> + pr_err("zbud: invalid buddy value %d\n", bud);
>> + handle = 0;
>> + break;
>> + }
>> return handle;
>> }
>>
>> @@ -287,6 +309,7 @@ static int num_free_chunks(struct zbud_header *zhdr)
>> /*
>> * Rather than branch for different situations, just use the fact that
>> * free buddies have a length of zero to simplify everything.
>> + * NB: can't be used with HEADLESS pages.
>> */
>> return NCHUNKS - zhdr->first_chunks - zhdr->last_chunks;
>> }
>> @@ -353,31 +376,40 @@ void zbud_destroy_pool(struct zbud_pool *pool)
>> int zbud_alloc(struct zbud_pool *pool, size_t size, gfp_t gfp,
>> unsigned long *handle)
>> {
>> - int chunks, i, freechunks;
>> + int chunks = 0, i, freechunks;
>> struct zbud_header *zhdr = NULL;
>> + struct zbud_page_priv *ppriv;
>> enum buddy bud;
>> struct page *page;
>>
>> if (!size || (gfp & __GFP_HIGHMEM))
>> return -EINVAL;
>> - if (size > PAGE_SIZE - ZHDR_SIZE_ALIGNED - CHUNK_SIZE)
>> +
>> + if (size > PAGE_SIZE)
>> return -ENOSPC;
>> - chunks = size_to_chunks(size);
>> - spin_lock(&pool->lock);
>>
>> - /* First, try to find an unbuddied zbud page. */
>> - zhdr = NULL;
>> - for_each_unbuddied_list(i, chunks) {
>> - if (!list_empty(&pool->unbuddied[i])) {
>> - zhdr = list_first_entry(&pool->unbuddied[i],
>> - struct zbud_header, buddy);
>> - list_del(&zhdr->buddy);
>> - if (zhdr->first_chunks == 0)
>> - bud = FIRST;
>> - else
>> - bud = LAST;
>> - goto found;
>> + if (size > PAGE_SIZE - ZHDR_SIZE_ALIGNED - CHUNK_SIZE)
>> + bud = HEADLESS;
>> + else {
>> + chunks = size_to_chunks(size);
>> + spin_lock(&pool->lock);
>> +
>> + /* First, try to find an unbuddied zbud page. */
>> + zhdr = NULL;
>> + for_each_unbuddied_list(i, chunks) {
>> + if (!list_empty(&pool->unbuddied[i])) {
>> + zhdr = list_first_entry(&pool->unbuddied[i],
>> + struct zbud_header, buddy);
>> + list_del(&zhdr->buddy);
>> + page = virt_to_page(zhdr);
>> + if (zhdr->first_chunks == 0)
>> + bud = FIRST;
>> + else
>> + bud = LAST;
>> + goto found;
>> + }
>> }
>> + bud = FIRST;
>> }
>>
>> /* Couldn't find unbuddied zbud page, create new one */
>> @@ -388,27 +420,31 @@ int zbud_alloc(struct zbud_pool *pool, size_t size, gfp_t gfp,
>> spin_lock(&pool->lock);
>> pool->pages_nr++;
>> zhdr = init_zbud_page(page);
>> - bud = FIRST;
>>
>> found:
>> - if (bud == FIRST)
>> - zhdr->first_chunks = chunks;
>> - else
>> - zhdr->last_chunks = chunks;
>> + ppriv = (struct zbud_page_priv *)page->private;
>> + if (bud != HEADLESS) {
>
> another personal opinion...it might look simpler if you just do:
>
> if (bud == FULL) {
> set_bit(ZBUD_FULL_PAGE, &page->private);
> goto full;
> }
Agreed here too.
>> + if (bud == FIRST)
>> + zhdr->first_chunks = chunks;
>> + else
>> + zhdr->last_chunks = chunks;
>> +
>> + if (zhdr->first_chunks == 0 || zhdr->last_chunks == 0) {
>> + /* Add to unbuddied list */
>> + freechunks = num_free_chunks(zhdr);
>> + list_add(&zhdr->buddy, &pool->unbuddied[freechunks]);
>> + } else {
>> + /* Add to buddied list */
>> + list_add(&zhdr->buddy, &pool->buddied);
>> + }
>>
>> - if (zhdr->first_chunks == 0 || zhdr->last_chunks == 0) {
>> - /* Add to unbuddied list */
>> - freechunks = num_free_chunks(zhdr);
>> - list_add(&zhdr->buddy, &pool->unbuddied[freechunks]);
>> - } else {
>> - /* Add to buddied list */
>> - list_add(&zhdr->buddy, &pool->buddied);
>> - }
>> + /* Add/move zbud page to beginning of LRU */
>> + if (!list_empty(&page->lru))
>> + list_del(&page->lru);
>> + } else
>> + ppriv->headless = true;
>>
>
> insert label here...
>
> full:
>
>> - /* Add/move zbud page to beginning of LRU */
>> - if (!list_empty(&zhdr->lru))
>> - list_del(&zhdr->lru);
>
> no matter the case, this is safe; leave it here for simplicity. a
> full page will have a empty list head.
>
>> - list_add(&zhdr->lru, &pool->lru);
>> + list_add(&page->lru, &pool->lru);
>>
>> *handle = encode_handle(zhdr, bud);
>> spin_unlock(&pool->lock);
>> @@ -430,28 +466,41 @@ void zbud_free(struct zbud_pool *pool, unsigned long handle)
>> {
>> struct zbud_header *zhdr;
>> int freechunks;
>> + struct page *page;
>> + enum buddy bud;
>> + struct zbud_page_priv *ppriv;
>>
>> spin_lock(&pool->lock);
>> zhdr = handle_to_zbud_header(handle);
>> + page = virt_to_page(zhdr);
>> + ppriv = (struct zbud_page_priv *)page->private;
>>
>> - /* If first buddy, handle will be page aligned */
>> - if ((handle - ZHDR_SIZE_ALIGNED) & ~PAGE_MASK)
>> + if (!(handle & ~PAGE_MASK)) /* HEADLESS page stored */
>> + bud = HEADLESS;
>> + else if ((handle - ZHDR_SIZE_ALIGNED) & ~PAGE_MASK) {
>> + bud = LAST;
>> zhdr->last_chunks = 0;
>> - else
>> + } else {
>> + /* If first buddy, handle will be page aligned */
>> + bud = FIRST;
>> zhdr->first_chunks = 0;
>> + }
>>
>> - if (zhdr->under_reclaim) {
>> + if (ppriv->under_reclaim) {
>> /* zbud page is under reclaim, reclaim will free */
>> spin_unlock(&pool->lock);
>> return;
>> }
>>
>> - /* Remove from existing buddy list */
>> - list_del(&zhdr->buddy);
>> + if (bud != HEADLESS) {
>> + /* Remove from existing buddy list */
>> + list_del(&zhdr->buddy);
>> + }
>>
>> - if (zhdr->first_chunks == 0 && zhdr->last_chunks == 0) {
>> + if (bud == HEADLESS ||
>> + (zhdr->first_chunks == 0 && zhdr->last_chunks == 0)) {
>> /* zbud page is empty, free */
>> - list_del(&zhdr->lru);
>> + list_del(&page->lru);
>> free_zbud_page(zhdr);
>> pool->pages_nr--;
>> } else {
>> @@ -505,6 +554,8 @@ int zbud_reclaim_page(struct zbud_pool *pool, unsigned int retries)
>> {
>> int i, ret, freechunks;
>> struct zbud_header *zhdr;
>> + struct page *page;
>> + struct zbud_page_priv *ppriv;
>> unsigned long first_handle = 0, last_handle = 0;
>>
>> spin_lock(&pool->lock);
>> @@ -514,21 +565,31 @@ int zbud_reclaim_page(struct zbud_pool *pool, unsigned int retries)
>> return -EINVAL;
>> }
>> for (i = 0; i < retries; i++) {
>> - zhdr = list_tail_entry(&pool->lru, struct zbud_header, lru);
>> - list_del(&zhdr->lru);
>> - list_del(&zhdr->buddy);
>> + page = list_tail_entry(&pool->lru, struct page, lru);
>> + ppriv = (struct zbud_page_priv *)page->private;
>> + list_del(&page->lru);
>> +
>> /* Protect zbud page against free */
>> - zhdr->under_reclaim = true;
>> - /*
>> - * We need encode the handles before unlocking, since we can
>> - * race with free that will set (first|last)_chunks to 0
>> - */
>> - first_handle = 0;
>> - last_handle = 0;
>> - if (zhdr->first_chunks)
>> - first_handle = encode_handle(zhdr, FIRST);
>> - if (zhdr->last_chunks)
>> - last_handle = encode_handle(zhdr, LAST);
>> + ppriv->under_reclaim = true;
>> + zhdr = page_address(page);
>> + if (!ppriv->headless) {
>> + list_del(&zhdr->buddy);
>> + /*
>> + * We need encode the handles before unlocking, since
>> + * we can race with free that will set
>> + * (first|last)_chunks to 0
>> + */
>> + first_handle = 0;
>> + last_handle = 0;
>> + if (zhdr->first_chunks)
>> + first_handle = encode_handle(zhdr, FIRST);
>> + if (zhdr->last_chunks)
>> + last_handle = encode_handle(zhdr, LAST);
>> + } else {
>> + first_handle = encode_handle(zhdr, HEADLESS);
>> + last_handle = 0;
>> + }
>> +
>> spin_unlock(&pool->lock);
>>
>> /* Issue the eviction callback(s) */
>> @@ -544,8 +605,9 @@ int zbud_reclaim_page(struct zbud_pool *pool, unsigned int retries)
>> }
>> next:
>> spin_lock(&pool->lock);
>> - zhdr->under_reclaim = false;
>> - if (zhdr->first_chunks == 0 && zhdr->last_chunks == 0) {
>> + ppriv->under_reclaim = false;
>> + if (ppriv->headless ||
>> + (zhdr->first_chunks == 0 && zhdr->last_chunks == 0)) {
>
> oops, this isn't right. you're assuming ->headless means the eviction
> succeeded. However if pool->ops->evict() failed, that isn't true.
Aha, good catch, thanks. Then it looks like we need separate handling
for the 'headless' case here, e. g.
if (ppriv->headless) {
if (ret == 0) {
free_zbud_page(zhdr);
pool->pages_nr--;
spin_unlock(&pool->lock);
}
} else if (zhdr->first_chunks == 0 && zhdr->last_chunks == 0) {
...
The block under 'if (ret == 0)' may also become a static inline to
avoid code duplication.
~vitaly
On Tue, Sep 22, 2015 at 11:49 PM, Dan Streetman <ddstreet@...e.org> wrote:
> On Tue, Sep 22, 2015 at 8:17 AM, Vitaly Wool <vitalywool@...il.com> wrote:
>> Currently zbud is only capable of allocating not more than
>> PAGE_SIZE - ZHDR_SIZE_ALIGNED - CHUNK_SIZE. This is okay as
>> long as only zswap is using it, but other users of zbud may
>> (and likely will) want to allocate up to PAGE_SIZE. This patch
>> addresses that by skipping the creation of zbud internal
>> structure in the beginning of an allocated page (such pages are
>> then called 'headless').
>>
>> As a zbud page is no longer guaranteed to contain zbud header, the
>> following changes had to be applied throughout the code:
>> * page->lru to be used for zbud page lists
>> * page->private to hold 'under_reclaim' flag
>>
>> page->private will also be used to indicate if this page contains
>> a zbud header in the beginning or not ('headless' flag).
>>
>> Signed-off-by: Vitaly Wool <vitalywool@...il.com>
>> ---
>> mm/zbud.c | 194 +++++++++++++++++++++++++++++++++++++++++---------------------
>> 1 file changed, 128 insertions(+), 66 deletions(-)
>>
>> diff --git a/mm/zbud.c b/mm/zbud.c
>> index fa48bcdf..7b51eb6 100644
>> --- a/mm/zbud.c
>> +++ b/mm/zbud.c
>> @@ -105,18 +105,25 @@ struct zbud_pool {
>>
>> /*
>> * struct zbud_header - zbud page metadata occupying the first chunk of each
>> - * zbud page.
>> + * zbud page, except for HEADLESS pages
>
> hmm, personally I like "FULL" better than HEADLESS...it's only
> headless because it's a full page.
>
>> * @buddy: links the zbud page into the unbuddied/buddied lists in the pool
>> - * @lru: links the zbud page into the lru list in the pool
>> * @first_chunks: the size of the first buddy in chunks, 0 if free
>> * @last_chunks: the size of the last buddy in chunks, 0 if free
>> */
>> struct zbud_header {
>> struct list_head buddy;
>> - struct list_head lru;
>> unsigned int first_chunks;
>> unsigned int last_chunks;
>> - bool under_reclaim;
>> +};
>> +
>> +/*
>> + * struct zbud_page_priv - zbud flags to be stored in page->private
>> + * @under_reclaim: if a zbud page is under reclaim
>> + * @headless: indicates a page where zbud header didn't fit
>> + */
>> +struct zbud_page_priv {
>> + bool under_reclaim:1;
>> + bool headless:1;
>> };
>
> Hmm, this is just my personal opinion, but I'm not a fan of casting
> ->private as a struct, if we're only using it as a bitmap. I'd
> suggest just defining bits as an enum (like page flags), e.g.
>
> enum zbud_flags {
> ZBUD_UNDER_RECLAIM,
> ZBUD_FULL_PAGE,
> };
>
> or some names similar to that. then it can be checked with a simple
> test_bit() call, and set_bit()/clear_bit().
>
> alternately, there are the already-existing PG_private and
> PG_private_2 bits in the page flags...but unless we need ->private for
> something else, it probably makes more sense to just use it instead of
> the PG_private flags.
>
>>
>> /*****************
>> @@ -221,6 +228,7 @@ MODULE_ALIAS("zpool-zbud");
>> *****************/
>> /* Just to make the code easier to read */
>> enum buddy {
>> + HEADLESS,
>> FIRST,
>> LAST
>> };
>> @@ -237,12 +245,15 @@ static int size_to_chunks(size_t size)
>> /* Initializes the zbud header of a newly allocated zbud page */
>> static struct zbud_header *init_zbud_page(struct page *page)
>> {
>> + struct zbud_page_priv *ppriv = (struct zbud_page_priv *)page->private;
>> struct zbud_header *zhdr = page_address(page);
>> +
>> + INIT_LIST_HEAD(&page->lru);
>> + ppriv->under_reclaim = 0;
>
> don't forget to initialize the headless/full bit too. (I'll mention
> that the page allocation code does clear ->private before handing it
> to us, so it should already be 0. but let's not rely on that)
>
>> +
>> zhdr->first_chunks = 0;
>> zhdr->last_chunks = 0;
>> INIT_LIST_HEAD(&zhdr->buddy);
>> - INIT_LIST_HEAD(&zhdr->lru);
>> - zhdr->under_reclaim = 0;
>> return zhdr;
>> }
>>
>> @@ -267,11 +278,22 @@ static unsigned long encode_handle(struct zbud_header *zhdr, enum buddy bud)
>> * over the zbud header in the first chunk.
>> */
>> handle = (unsigned long)zhdr;
>> - if (bud == FIRST)
>> + switch (bud) {
>> + case FIRST:
>> /* skip over zbud header */
>> handle += ZHDR_SIZE_ALIGNED;
>> - else /* bud == LAST */
>> + break;
>> + case LAST:
>> handle += PAGE_SIZE - (zhdr->last_chunks << CHUNK_SHIFT);
>> + break;
>> + case HEADLESS:
>> + break;
>> + default:
>> + /* this should never happen */
>> + pr_err("zbud: invalid buddy value %d\n", bud);
>> + handle = 0;
>> + break;
>> + }
>> return handle;
>> }
>>
>> @@ -287,6 +309,7 @@ static int num_free_chunks(struct zbud_header *zhdr)
>> /*
>> * Rather than branch for different situations, just use the fact that
>> * free buddies have a length of zero to simplify everything.
>> + * NB: can't be used with HEADLESS pages.
>> */
>> return NCHUNKS - zhdr->first_chunks - zhdr->last_chunks;
>> }
>> @@ -353,31 +376,40 @@ void zbud_destroy_pool(struct zbud_pool *pool)
>> int zbud_alloc(struct zbud_pool *pool, size_t size, gfp_t gfp,
>> unsigned long *handle)
>> {
>> - int chunks, i, freechunks;
>> + int chunks = 0, i, freechunks;
>> struct zbud_header *zhdr = NULL;
>> + struct zbud_page_priv *ppriv;
>> enum buddy bud;
>> struct page *page;
>>
>> if (!size || (gfp & __GFP_HIGHMEM))
>> return -EINVAL;
>> - if (size > PAGE_SIZE - ZHDR_SIZE_ALIGNED - CHUNK_SIZE)
>> +
>> + if (size > PAGE_SIZE)
>> return -ENOSPC;
>> - chunks = size_to_chunks(size);
>> - spin_lock(&pool->lock);
>>
>> - /* First, try to find an unbuddied zbud page. */
>> - zhdr = NULL;
>> - for_each_unbuddied_list(i, chunks) {
>> - if (!list_empty(&pool->unbuddied[i])) {
>> - zhdr = list_first_entry(&pool->unbuddied[i],
>> - struct zbud_header, buddy);
>> - list_del(&zhdr->buddy);
>> - if (zhdr->first_chunks == 0)
>> - bud = FIRST;
>> - else
>> - bud = LAST;
>> - goto found;
>> + if (size > PAGE_SIZE - ZHDR_SIZE_ALIGNED - CHUNK_SIZE)
>> + bud = HEADLESS;
>> + else {
>> + chunks = size_to_chunks(size);
>> + spin_lock(&pool->lock);
>> +
>> + /* First, try to find an unbuddied zbud page. */
>> + zhdr = NULL;
>> + for_each_unbuddied_list(i, chunks) {
>> + if (!list_empty(&pool->unbuddied[i])) {
>> + zhdr = list_first_entry(&pool->unbuddied[i],
>> + struct zbud_header, buddy);
>> + list_del(&zhdr->buddy);
>> + page = virt_to_page(zhdr);
>> + if (zhdr->first_chunks == 0)
>> + bud = FIRST;
>> + else
>> + bud = LAST;
>> + goto found;
>> + }
>> }
>> + bud = FIRST;
>> }
>>
>> /* Couldn't find unbuddied zbud page, create new one */
>> @@ -388,27 +420,31 @@ int zbud_alloc(struct zbud_pool *pool, size_t size, gfp_t gfp,
>> spin_lock(&pool->lock);
>> pool->pages_nr++;
>> zhdr = init_zbud_page(page);
>> - bud = FIRST;
>>
>> found:
>> - if (bud == FIRST)
>> - zhdr->first_chunks = chunks;
>> - else
>> - zhdr->last_chunks = chunks;
>> + ppriv = (struct zbud_page_priv *)page->private;
>> + if (bud != HEADLESS) {
>
> another personal opinion...it might look simpler if you just do:
>
> if (bud == FULL) {
> set_bit(ZBUD_FULL_PAGE, &page->private);
> goto full;
> }
>
>> + if (bud == FIRST)
>> + zhdr->first_chunks = chunks;
>> + else
>> + zhdr->last_chunks = chunks;
>> +
>> + if (zhdr->first_chunks == 0 || zhdr->last_chunks == 0) {
>> + /* Add to unbuddied list */
>> + freechunks = num_free_chunks(zhdr);
>> + list_add(&zhdr->buddy, &pool->unbuddied[freechunks]);
>> + } else {
>> + /* Add to buddied list */
>> + list_add(&zhdr->buddy, &pool->buddied);
>> + }
>>
>> - if (zhdr->first_chunks == 0 || zhdr->last_chunks == 0) {
>> - /* Add to unbuddied list */
>> - freechunks = num_free_chunks(zhdr);
>> - list_add(&zhdr->buddy, &pool->unbuddied[freechunks]);
>> - } else {
>> - /* Add to buddied list */
>> - list_add(&zhdr->buddy, &pool->buddied);
>> - }
>> + /* Add/move zbud page to beginning of LRU */
>> + if (!list_empty(&page->lru))
>> + list_del(&page->lru);
>> + } else
>> + ppriv->headless = true;
>>
>
> insert label here...
>
> full:
>
>> - /* Add/move zbud page to beginning of LRU */
>> - if (!list_empty(&zhdr->lru))
>> - list_del(&zhdr->lru);
>
> no matter the case, this is safe; leave it here for simplicity. a
> full page will have a empty list head.
>
>> - list_add(&zhdr->lru, &pool->lru);
>> + list_add(&page->lru, &pool->lru);
>>
>> *handle = encode_handle(zhdr, bud);
>> spin_unlock(&pool->lock);
>> @@ -430,28 +466,41 @@ void zbud_free(struct zbud_pool *pool, unsigned long handle)
>> {
>> struct zbud_header *zhdr;
>> int freechunks;
>> + struct page *page;
>> + enum buddy bud;
>> + struct zbud_page_priv *ppriv;
>>
>> spin_lock(&pool->lock);
>> zhdr = handle_to_zbud_header(handle);
>> + page = virt_to_page(zhdr);
>> + ppriv = (struct zbud_page_priv *)page->private;
>>
>> - /* If first buddy, handle will be page aligned */
>> - if ((handle - ZHDR_SIZE_ALIGNED) & ~PAGE_MASK)
>> + if (!(handle & ~PAGE_MASK)) /* HEADLESS page stored */
>> + bud = HEADLESS;
>> + else if ((handle - ZHDR_SIZE_ALIGNED) & ~PAGE_MASK) {
>> + bud = LAST;
>> zhdr->last_chunks = 0;
>> - else
>> + } else {
>> + /* If first buddy, handle will be page aligned */
>> + bud = FIRST;
>> zhdr->first_chunks = 0;
>> + }
>>
>> - if (zhdr->under_reclaim) {
>> + if (ppriv->under_reclaim) {
>> /* zbud page is under reclaim, reclaim will free */
>> spin_unlock(&pool->lock);
>> return;
>> }
>>
>> - /* Remove from existing buddy list */
>> - list_del(&zhdr->buddy);
>> + if (bud != HEADLESS) {
>> + /* Remove from existing buddy list */
>> + list_del(&zhdr->buddy);
>> + }
>>
>> - if (zhdr->first_chunks == 0 && zhdr->last_chunks == 0) {
>> + if (bud == HEADLESS ||
>> + (zhdr->first_chunks == 0 && zhdr->last_chunks == 0)) {
>> /* zbud page is empty, free */
>> - list_del(&zhdr->lru);
>> + list_del(&page->lru);
>> free_zbud_page(zhdr);
>> pool->pages_nr--;
>> } else {
>> @@ -505,6 +554,8 @@ int zbud_reclaim_page(struct zbud_pool *pool, unsigned int retries)
>> {
>> int i, ret, freechunks;
>> struct zbud_header *zhdr;
>> + struct page *page;
>> + struct zbud_page_priv *ppriv;
>> unsigned long first_handle = 0, last_handle = 0;
>>
>> spin_lock(&pool->lock);
>> @@ -514,21 +565,31 @@ int zbud_reclaim_page(struct zbud_pool *pool, unsigned int retries)
>> return -EINVAL;
>> }
>> for (i = 0; i < retries; i++) {
>> - zhdr = list_tail_entry(&pool->lru, struct zbud_header, lru);
>> - list_del(&zhdr->lru);
>> - list_del(&zhdr->buddy);
>> + page = list_tail_entry(&pool->lru, struct page, lru);
>> + ppriv = (struct zbud_page_priv *)page->private;
>> + list_del(&page->lru);
>> +
>> /* Protect zbud page against free */
>> - zhdr->under_reclaim = true;
>> - /*
>> - * We need encode the handles before unlocking, since we can
>> - * race with free that will set (first|last)_chunks to 0
>> - */
>> - first_handle = 0;
>> - last_handle = 0;
>> - if (zhdr->first_chunks)
>> - first_handle = encode_handle(zhdr, FIRST);
>> - if (zhdr->last_chunks)
>> - last_handle = encode_handle(zhdr, LAST);
>> + ppriv->under_reclaim = true;
>> + zhdr = page_address(page);
>> + if (!ppriv->headless) {
>> + list_del(&zhdr->buddy);
>> + /*
>> + * We need encode the handles before unlocking, since
>> + * we can race with free that will set
>> + * (first|last)_chunks to 0
>> + */
>> + first_handle = 0;
>> + last_handle = 0;
>> + if (zhdr->first_chunks)
>> + first_handle = encode_handle(zhdr, FIRST);
>> + if (zhdr->last_chunks)
>> + last_handle = encode_handle(zhdr, LAST);
>> + } else {
>> + first_handle = encode_handle(zhdr, HEADLESS);
>> + last_handle = 0;
>> + }
>> +
>> spin_unlock(&pool->lock);
>>
>> /* Issue the eviction callback(s) */
>> @@ -544,8 +605,9 @@ int zbud_reclaim_page(struct zbud_pool *pool, unsigned int retries)
>> }
>> next:
>> spin_lock(&pool->lock);
>> - zhdr->under_reclaim = false;
>> - if (zhdr->first_chunks == 0 && zhdr->last_chunks == 0) {
>> + ppriv->under_reclaim = false;
>> + if (ppriv->headless ||
>> + (zhdr->first_chunks == 0 && zhdr->last_chunks == 0)) {
>
> oops, this isn't right. you're assuming ->headless means the eviction
> succeeded. However if pool->ops->evict() failed, that isn't true.
>
>> /*
>> * Both buddies are now free, free the zbud page and
>> * return success.
>> @@ -565,7 +627,7 @@ next:
>> }
>>
>> /* add to beginning of LRU */
>> - list_add(&zhdr->lru, &pool->lru);
>> + list_add(&page->lru, &pool->lru);
>> }
>> spin_unlock(&pool->lock);
>> return -EAGAIN;
>> --
>> 2.4.2
>>
--
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