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Message-ID: <8e0800ee-9945-4c16-9b22-a385ddb1f13a@bytedance.com>
Date: Wed, 13 Dec 2023 10:46:39 +0800
From: Chengming Zhou <zhouchengming@...edance.com>
To: Nhat Pham <nphamcs@...il.com>
Cc: Vitaly Wool <vitaly.wool@...sulko.com>,
Johannes Weiner <hannes@...xchg.org>,
Michal Hocko <mhocko@...nel.org>,
Seth Jennings <sjenning@...hat.com>,
Dan Streetman <ddstreet@...e.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Yosry Ahmed <yosryahmed@...gle.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/7] mm/zswap: refactor out __zswap_load()
On 2023/12/13 07:13, Nhat Pham wrote:
> On Wed, Dec 6, 2023 at 1:46 AM Chengming Zhou
> <zhouchengming@...edance.com> wrote:
>>
>> The zswap_load() and zswap_writeback_entry() have the same part that
>> decompress the data from zswap_entry to page, so refactor out the
>> common part as __zswap_load(entry, page).
>
> I love this refactoring a lot :) No reason why we should duplicate the
> decompression logic shared between load and writeback.
>
>>
>> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
>> ---
>> mm/zswap.c | 108 ++++++++++++++++++++++---------------------------------------
>> 1 file changed, 39 insertions(+), 69 deletions(-)
>>
>> diff --git a/mm/zswap.c b/mm/zswap.c
>> index 999671dcb469..667b66a3911b 100644
>> --- a/mm/zswap.c
>> +++ b/mm/zswap.c
>> @@ -1380,6 +1380,42 @@ static int zswap_enabled_param_set(const char *val,
>> return ret;
>> }
>>
>> +static void __zswap_load(struct zswap_entry *entry, struct page *page)
>> +{
>> + struct scatterlist input, output;
>> + unsigned int dlen = PAGE_SIZE;
>> + struct crypto_acomp_ctx *acomp_ctx;
>> + struct zpool *zpool;
>> + u8 *src;
>> + int ret;
>> +
>> + /* decompress */
>
> nit: I guess all this function does is decompression right? Doesn't
> seem like this comment is necessary anymore... But this is just
> nitpicking.
>
Ah, right. I will remove it.
Thanks!
>> + acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
>> + mutex_lock(acomp_ctx->mutex);
>> +
>> + zpool = zswap_find_zpool(entry);
>> + src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO);
>> + if (!zpool_can_sleep_mapped(zpool)) {
>> + memcpy(acomp_ctx->dstmem, src, entry->length);
>> + src = acomp_ctx->dstmem;
>> + zpool_unmap_handle(zpool, entry->handle);
>> + }
>> +
>> + sg_init_one(&input, src, entry->length);
>> + sg_init_table(&output, 1);
>> + sg_set_page(&output, page, PAGE_SIZE, 0);
>> + acomp_request_set_params(acomp_ctx->req, &input, &output, entry->length, dlen);
>> + ret = crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait);
>> + dlen = acomp_ctx->req->dlen;
>> + mutex_unlock(acomp_ctx->mutex);
>> +
>> + if (zpool_can_sleep_mapped(zpool))
>> + zpool_unmap_handle(zpool, entry->handle);
>> +
>> + BUG_ON(ret);
>> + BUG_ON(dlen != PAGE_SIZE);
>> +}
>> +
>> /*********************************
>> * writeback code
>> **********************************/
>> @@ -1401,23 +1437,12 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
>> swp_entry_t swpentry = entry->swpentry;
>> struct page *page;
>> struct mempolicy *mpol;
>> - struct scatterlist input, output;
>> - struct crypto_acomp_ctx *acomp_ctx;
>> - struct zpool *pool = zswap_find_zpool(entry);
>> bool page_was_allocated;
>> - u8 *src, *tmp = NULL;
>> - unsigned int dlen;
>> int ret;
>> struct writeback_control wbc = {
>> .sync_mode = WB_SYNC_NONE,
>> };
>>
>> - if (!zpool_can_sleep_mapped(pool)) {
>> - tmp = kmalloc(PAGE_SIZE, GFP_KERNEL);
>> - if (!tmp)
>> - return -ENOMEM;
>> - }
>> -
>
> Sweet. Less allocation == more efficient + less failure case :)
>
>> /* try to allocate swap cache page */
>> mpol = get_task_policy(current);
>> page = __read_swap_cache_async(swpentry, GFP_KERNEL, mpol,
>> @@ -1450,33 +1475,7 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
>> }
>> spin_unlock(&tree->lock);
>>
>> - /* decompress */
>> - acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
>> - dlen = PAGE_SIZE;
>> -
>> - src = zpool_map_handle(pool, entry->handle, ZPOOL_MM_RO);
>> - if (!zpool_can_sleep_mapped(pool)) {
>> - memcpy(tmp, src, entry->length);
>> - src = tmp;
>> - zpool_unmap_handle(pool, entry->handle);
>> - }
>> -
>> - mutex_lock(acomp_ctx->mutex);
>> - sg_init_one(&input, src, entry->length);
>> - sg_init_table(&output, 1);
>> - sg_set_page(&output, page, PAGE_SIZE, 0);
>> - acomp_request_set_params(acomp_ctx->req, &input, &output, entry->length, dlen);
>> - ret = crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait);
>> - dlen = acomp_ctx->req->dlen;
>> - mutex_unlock(acomp_ctx->mutex);
>> -
>> - if (!zpool_can_sleep_mapped(pool))
>> - kfree(tmp);
>> - else
>> - zpool_unmap_handle(pool, entry->handle);
>> -
>> - BUG_ON(ret);
>> - BUG_ON(dlen != PAGE_SIZE);
>> + __zswap_load(entry, page);
>>
>> /* page is up to date */
>> SetPageUptodate(page);
>> @@ -1496,9 +1495,6 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
>> return ret;
>>
>> fail:
>> - if (!zpool_can_sleep_mapped(pool))
>> - kfree(tmp);
>> -
>> /*
>> * If we get here because the page is already in swapcache, a
>> * load may be happening concurrently. It is safe and okay to
>> @@ -1755,11 +1751,7 @@ bool zswap_load(struct folio *folio)
>> struct page *page = &folio->page;
>> struct zswap_tree *tree = swap_zswap_tree(swp);
>> struct zswap_entry *entry;
>> - struct scatterlist input, output;
>> - struct crypto_acomp_ctx *acomp_ctx;
>> - unsigned int dlen = PAGE_SIZE;
>> - u8 *src, *dst;
>> - struct zpool *zpool;
>> + u8 *dst;
>> bool ret;
>>
>> VM_WARN_ON_ONCE(!folio_test_locked(folio));
>> @@ -1781,29 +1773,7 @@ bool zswap_load(struct folio *folio)
>> goto stats;
>> }
>>
>> - /* decompress */
>> - acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
>> - mutex_lock(acomp_ctx->mutex);
>> -
>> - zpool = zswap_find_zpool(entry);
>> - src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO);
>> - if (!zpool_can_sleep_mapped(zpool)) {
>> - memcpy(acomp_ctx->dstmem, src, entry->length);
>> - src = acomp_ctx->dstmem;
>> - zpool_unmap_handle(zpool, entry->handle);
>> - }
>> -
>> - sg_init_one(&input, src, entry->length);
>> - sg_init_table(&output, 1);
>> - sg_set_page(&output, page, PAGE_SIZE, 0);
>> - acomp_request_set_params(acomp_ctx->req, &input, &output, entry->length, dlen);
>> - if (crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait))
>> - WARN_ON(1);
>> - mutex_unlock(acomp_ctx->mutex);
>> -
>> - if (zpool_can_sleep_mapped(zpool))
>> - zpool_unmap_handle(zpool, entry->handle);
>> -
>> + __zswap_load(entry, page);
>> ret = true;
>> stats:
>> count_vm_event(ZSWPIN);
>>
>> --
>> b4 0.10.1
>
> Can't find anything wrong with this patch, so:
> Reviewed-by: Nhat Pham <nphamcs@...il.com>
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