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Message-ID: <516BB4C6.8090101@citrix.com>
Date: Mon, 15 Apr 2013 10:05:26 +0200
From: Roger Pau Monné <roger.pau@...rix.com>
To: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>
Subject: Re: [PATCH v1 2/7] xen-blkback: use balloon pages for all mappings
On 09/04/13 16:47, Konrad Rzeszutek Wilk wrote:
> On Wed, Mar 27, 2013 at 12:10:38PM +0100, Roger Pau Monne wrote:
>> Using balloon pages for all granted pages allows us to simplify the
>> logic in blkback, especially in the xen_blkbk_map function, since now
>> we can decide if we want to map a grant persistently or not after we
>> have actually mapped it. This could not be done before because
>> persistent grants used ballooned pages, whereas non-persistent grants
>> used pages from the kernel.
>>
>> This patch also introduces several changes, the first one is that the
>> list of free pages is no longer global, now each blkback instance has
>> it's own list of free pages that can be used to map grants. Also, a
>> run time parameter (max_buffer_pages) has been added in order to tune
>> the maximum number of free pages each blkback instance will keep in
>> it's buffer.
>>
>> Signed-off-by: Roger Pau Monné <roger.pau@...rix.com>
>> Cc: xen-devel@...ts.xen.org
>> Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
>
> Sorry for the late review. Some comments.
Thanks for the review.
>> ---
>> Changes since RFC:
>> * Fix typos in commit message.
>> * Minor fixes in code.
>> ---
>> Documentation/ABI/stable/sysfs-bus-xen-backend | 8 +
>> drivers/block/xen-blkback/blkback.c | 265 +++++++++++++-----------
>> drivers/block/xen-blkback/common.h | 5 +
>> drivers/block/xen-blkback/xenbus.c | 3 +
>> 4 files changed, 165 insertions(+), 116 deletions(-)
>>
>> diff --git a/Documentation/ABI/stable/sysfs-bus-xen-backend b/Documentation/ABI/stable/sysfs-bus-xen-backend
>> index 3d5951c..e04afe0 100644
>> --- a/Documentation/ABI/stable/sysfs-bus-xen-backend
>> +++ b/Documentation/ABI/stable/sysfs-bus-xen-backend
>> @@ -73,3 +73,11 @@ KernelVersion: 3.0
>> Contact: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
>> Description:
>> Number of sectors written by the frontend.
>> +
>> +What: /sys/module/xen_blkback/parameters/max_buffer_pages
>> +Date: March 2013
>> +KernelVersion: 3.10
>> +Contact: Roger Pau Monné <roger.pau@...rix.com>
>> +Description:
>> + Maximum number of free pages to keep in each block
>> + backend buffer.
>> diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
>> index f7526db..8a1892a 100644
>> --- a/drivers/block/xen-blkback/blkback.c
>> +++ b/drivers/block/xen-blkback/blkback.c
>> @@ -63,6 +63,21 @@ static int xen_blkif_reqs = 64;
>> module_param_named(reqs, xen_blkif_reqs, int, 0);
>> MODULE_PARM_DESC(reqs, "Number of blkback requests to allocate");
>>
>> +/*
>> + * Maximum number of unused free pages to keep in the internal buffer.
>> + * Setting this to a value too low will reduce memory used in each backend,
>> + * but can have a performance penalty.
>> + *
>> + * A sane value is xen_blkif_reqs * BLKIF_MAX_SEGMENTS_PER_REQUEST, but can
>> + * be set to a lower value that might degrade performance on some intensive
>> + * IO workloads.
>> + */
>> +
>> +static int xen_blkif_max_buffer_pages = 704;
>> +module_param_named(max_buffer_pages, xen_blkif_max_buffer_pages, int, 0644);
>> +MODULE_PARM_DESC(max_buffer_pages,
>> +"Maximum number of free pages to keep in each block backend buffer");
>> +
>> /* Run-time switchable: /sys/module/blkback/parameters/ */
>> static unsigned int log_stats;
>> module_param(log_stats, int, 0644);
>> @@ -82,10 +97,14 @@ struct pending_req {
>> int status;
>> struct list_head free_list;
>> DECLARE_BITMAP(unmap_seg, BLKIF_MAX_SEGMENTS_PER_REQUEST);
>> + struct page *pages[BLKIF_MAX_SEGMENTS_PER_REQUEST];
>> };
>>
>> #define BLKBACK_INVALID_HANDLE (~0)
>>
>> +/* Number of free pages to remove on each call to free_xenballooned_pages */
>> +#define NUM_BATCH_FREE_PAGES 10
>> +
>> struct xen_blkbk {
>> struct pending_req *pending_reqs;
>> /* List of all 'pending_req' available */
>> @@ -93,8 +112,6 @@ struct xen_blkbk {
>> /* And its spinlock. */
>> spinlock_t pending_free_lock;
>> wait_queue_head_t pending_free_wq;
>> - /* The list of all pages that are available. */
>> - struct page **pending_pages;
>> /* And the grant handles that are available. */
>> grant_handle_t *pending_grant_handles;
>> };
>> @@ -143,14 +160,66 @@ static inline int vaddr_pagenr(struct pending_req *req, int seg)
>> BLKIF_MAX_SEGMENTS_PER_REQUEST + seg;
>> }
>>
>> -#define pending_page(req, seg) pending_pages[vaddr_pagenr(req, seg)]
>> +static inline int get_free_page(struct xen_blkif *blkif, struct page **page)
>> +{
>> + unsigned long flags;
>> +
>> + spin_lock_irqsave(&blkif->free_pages_lock, flags);
>
> I am curious to why you need to use the irqsave variant one here, as
>> + if (list_empty(&blkif->free_pages)) {
>> + BUG_ON(blkif->free_pages_num != 0);
>> + spin_unlock_irqrestore(&blkif->free_pages_lock, flags);
>> + return alloc_xenballooned_pages(1, page, false);
>
> This function is using an mutex.
>
> which would imply it is OK to have an non-irq variant of spinlock?
Yes, the only one that probably needs irqsave is put_free_pages, which
is not using any mutexes and could indeed be called from irq context.
>
>> + }
>> + BUG_ON(blkif->free_pages_num == 0);
>> + page[0] = list_first_entry(&blkif->free_pages, struct page, lru);
>> + list_del(&page[0]->lru);
>> + blkif->free_pages_num--;
>> + spin_unlock_irqrestore(&blkif->free_pages_lock, flags);
>> +
>> + return 0;
>> +}
>> +
>> +static inline void put_free_pages(struct xen_blkif *blkif, struct page **page,
>> + int num)
>> +{
>> + unsigned long flags;
>> + int i;
>> +
>> + spin_lock_irqsave(&blkif->free_pages_lock, flags);
>> + for (i = 0; i < num; i++)
>> + list_add(&page[i]->lru, &blkif->free_pages);
>> + blkif->free_pages_num += num;
>> + spin_unlock_irqrestore(&blkif->free_pages_lock, flags);
>> +}
>>
>> -static inline unsigned long vaddr(struct pending_req *req, int seg)
>> +static inline void shrink_free_pagepool(struct xen_blkif *blkif, int num)
>> {
>> - unsigned long pfn = page_to_pfn(blkbk->pending_page(req, seg));
>> - return (unsigned long)pfn_to_kaddr(pfn);
>> + /* Remove requested pages in batches of NUM_BATCH_FREE_PAGES */
>> + struct page *page[NUM_BATCH_FREE_PAGES];
>> + unsigned long flags;
>> + unsigned int num_pages = 0;
>> +
>> + spin_lock_irqsave(&blkif->free_pages_lock, flags);
>> + while (blkif->free_pages_num > num) {
>> + BUG_ON(list_empty(&blkif->free_pages));
>> + page[num_pages] = list_first_entry(&blkif->free_pages,
>> + struct page, lru);
>> + list_del(&page[num_pages]->lru);
>> + blkif->free_pages_num--;
>> + if (++num_pages == NUM_BATCH_FREE_PAGES) {
>> + spin_unlock_irqrestore(&blkif->free_pages_lock, flags);
>> + free_xenballooned_pages(num_pages, page);
>> + spin_lock_irqsave(&blkif->free_pages_lock, flags);
>> + num_pages = 0;
>> + }
>> + }
>> + spin_unlock_irqrestore(&blkif->free_pages_lock, flags);
>> + if (num_pages != 0)
>> + free_xenballooned_pages(num_pages, page);
>> }
>>
>> +#define vaddr(page) ((unsigned long)pfn_to_kaddr(page_to_pfn(page)))
>> +
>> #define pending_handle(_req, _seg) \
>> (blkbk->pending_grant_handles[vaddr_pagenr(_req, _seg)])
>>
>> @@ -170,7 +239,7 @@ static void make_response(struct xen_blkif *blkif, u64 id,
>> (n) = (&(pos)->node != NULL) ? rb_next(&(pos)->node) : NULL)
>>
>>
>> -static void add_persistent_gnt(struct rb_root *root,
>> +static int add_persistent_gnt(struct rb_root *root,
>> struct persistent_gnt *persistent_gnt)
>> {
>> struct rb_node **new = &(root->rb_node), *parent = NULL;
>> @@ -186,14 +255,15 @@ static void add_persistent_gnt(struct rb_root *root,
>> else if (persistent_gnt->gnt > this->gnt)
>> new = &((*new)->rb_right);
>> else {
>> - pr_alert(DRV_PFX " trying to add a gref that's already in the tree\n");
>> - BUG();
>> + pr_alert_ratelimited(DRV_PFX " trying to add a gref that's already in the tree\n");
>> + return -EINVAL;
>> }
>> }
>>
>> /* Add new node and rebalance tree. */
>> rb_link_node(&(persistent_gnt->node), parent, new);
>> rb_insert_color(&(persistent_gnt->node), root);
>> + return 0;
>> }
>>
>> static struct persistent_gnt *get_persistent_gnt(struct rb_root *root,
>> @@ -215,7 +285,8 @@ static struct persistent_gnt *get_persistent_gnt(struct rb_root *root,
>> return NULL;
>> }
>>
>> -static void free_persistent_gnts(struct rb_root *root, unsigned int num)
>> +static void free_persistent_gnts(struct xen_blkif *blkif, struct rb_root *root,
>> + unsigned int num)
>> {
>> struct gnttab_unmap_grant_ref unmap[BLKIF_MAX_SEGMENTS_PER_REQUEST];
>> struct page *pages[BLKIF_MAX_SEGMENTS_PER_REQUEST];
>> @@ -240,7 +311,7 @@ static void free_persistent_gnts(struct rb_root *root, unsigned int num)
>> ret = gnttab_unmap_refs(unmap, NULL, pages,
>> segs_to_unmap);
>> BUG_ON(ret);
>> - free_xenballooned_pages(segs_to_unmap, pages);
>> + put_free_pages(blkif, pages, segs_to_unmap);
>> segs_to_unmap = 0;
>> }
>>
>> @@ -422,13 +493,17 @@ int xen_blkif_schedule(void *arg)
>> if (do_block_io_op(blkif))
>> blkif->waiting_reqs = 1;
>>
>> + shrink_free_pagepool(blkif, xen_blkif_max_buffer_pages);
>
> That threw me off the first time I saw it. I somehow thought it meant
> to shrink all xen_blkif_max_buffer_pages, not the value "above" it.
>
> Might need a comment saying: "/* Shrink if we have more than xen_blkif_max_buffer_pages. */"
>
>
>> +
>> if (log_stats && time_after(jiffies, blkif->st_print))
>> print_stats(blkif);
>> }
>>
>> + shrink_free_pagepool(blkif, 0);
>
> Add a little comment by the zero please that says: /* All */
Done.
>
>> +
>> /* Free all persistent grant pages */
>> if (!RB_EMPTY_ROOT(&blkif->persistent_gnts))
>> - free_persistent_gnts(&blkif->persistent_gnts,
>> + free_persistent_gnts(blkif, &blkif->persistent_gnts,
>> blkif->persistent_gnt_c);
>>
>> BUG_ON(!RB_EMPTY_ROOT(&blkif->persistent_gnts));
>> @@ -457,23 +532,25 @@ static void xen_blkbk_unmap(struct pending_req *req)
>> struct page *pages[BLKIF_MAX_SEGMENTS_PER_REQUEST];
>> unsigned int i, invcount = 0;
>> grant_handle_t handle;
>> + struct xen_blkif *blkif = req->blkif;
>> int ret;
>>
>> for (i = 0; i < req->nr_pages; i++) {
>> if (!test_bit(i, req->unmap_seg))
>> continue;
>> handle = pending_handle(req, i);
>> + pages[invcount] = req->pages[i];
>> if (handle == BLKBACK_INVALID_HANDLE)
>> continue;
>> - gnttab_set_unmap_op(&unmap[invcount], vaddr(req, i),
>> + gnttab_set_unmap_op(&unmap[invcount], vaddr(pages[invcount]),
>> GNTMAP_host_map, handle);
>> pending_handle(req, i) = BLKBACK_INVALID_HANDLE;
>> - pages[invcount] = virt_to_page(vaddr(req, i));
>> invcount++;
>> }
>>
>> ret = gnttab_unmap_refs(unmap, NULL, pages, invcount);
>> BUG_ON(ret);
>> + put_free_pages(blkif, pages, invcount);
>> }
>>
>> static int xen_blkbk_map(struct blkif_request *req,
>> @@ -488,7 +565,6 @@ static int xen_blkbk_map(struct blkif_request *req,
>> struct xen_blkif *blkif = pending_req->blkif;
>> phys_addr_t addr = 0;
>> int i, j;
>> - bool new_map;
>> int nseg = req->u.rw.nr_segments;
>> int segs_to_map = 0;
>> int ret = 0;
>> @@ -517,68 +593,16 @@ static int xen_blkbk_map(struct blkif_request *req,
>> * We are using persistent grants and
>> * the grant is already mapped
>> */
>> - new_map = false;
>> - } else if (use_persistent_gnts &&
>> - blkif->persistent_gnt_c <
>> - max_mapped_grant_pages(blkif->blk_protocol)) {
>> - /*
>> - * We are using persistent grants, the grant is
>> - * not mapped but we have room for it
>> - */
>> - new_map = true;
>> - persistent_gnt = kmalloc(
>> - sizeof(struct persistent_gnt),
>> - GFP_KERNEL);
>> - if (!persistent_gnt)
>> - return -ENOMEM;
>> - if (alloc_xenballooned_pages(1, &persistent_gnt->page,
>> - false)) {
>> - kfree(persistent_gnt);
>> - return -ENOMEM;
>> - }
>> - persistent_gnt->gnt = req->u.rw.seg[i].gref;
>> - persistent_gnt->handle = BLKBACK_INVALID_HANDLE;
>> -
>> - pages_to_gnt[segs_to_map] =
>> - persistent_gnt->page;
>> - addr = (unsigned long) pfn_to_kaddr(
>> - page_to_pfn(persistent_gnt->page));
>> -
>> - add_persistent_gnt(&blkif->persistent_gnts,
>> - persistent_gnt);
>> - blkif->persistent_gnt_c++;
>> - pr_debug(DRV_PFX " grant %u added to the tree of persistent grants, using %u/%u\n",
>> - persistent_gnt->gnt, blkif->persistent_gnt_c,
>> - max_mapped_grant_pages(blkif->blk_protocol));
>> - } else {
>> - /*
>> - * We are either using persistent grants and
>> - * hit the maximum limit of grants mapped,
>> - * or we are not using persistent grants.
>> - */
>> - if (use_persistent_gnts &&
>> - !blkif->vbd.overflow_max_grants) {
>> - blkif->vbd.overflow_max_grants = 1;
>> - pr_alert(DRV_PFX " domain %u, device %#x is using maximum number of persistent grants\n",
>> - blkif->domid, blkif->vbd.handle);
>> - }
>> - new_map = true;
>> - pages[i] = blkbk->pending_page(pending_req, i);
>> - addr = vaddr(pending_req, i);
>> - pages_to_gnt[segs_to_map] =
>> - blkbk->pending_page(pending_req, i);
>> - }
>> -
>> - if (persistent_gnt) {
>
> Nice :-)
>
>> pages[i] = persistent_gnt->page;
>> persistent_gnts[i] = persistent_gnt;
>> } else {
>> + if (get_free_page(blkif, &pages[i]))
>> + goto out_of_memory;
>> + addr = vaddr(pages[i]);
>> + pages_to_gnt[segs_to_map] = pages[i];
>> persistent_gnts[i] = NULL;
>> - }
>> -
>> - if (new_map) {
>> flags = GNTMAP_host_map;
>> - if (!persistent_gnt &&
>> + if (!use_persistent_gnts &&
>> (pending_req->operation != BLKIF_OP_READ))
>> flags |= GNTMAP_readonly;
>> gnttab_set_map_op(&map[segs_to_map++], addr,
>> @@ -599,47 +623,71 @@ static int xen_blkbk_map(struct blkif_request *req,
>> */
>> bitmap_zero(pending_req->unmap_seg, BLKIF_MAX_SEGMENTS_PER_REQUEST);
>> for (i = 0, j = 0; i < nseg; i++) {
>> - if (!persistent_gnts[i] ||
>> - persistent_gnts[i]->handle == BLKBACK_INVALID_HANDLE) {
>> + if (!persistent_gnts[i]) {
>> /* This is a newly mapped grant */
>> BUG_ON(j >= segs_to_map);
>> if (unlikely(map[j].status != 0)) {
>> pr_debug(DRV_PFX "invalid buffer -- could not remap it\n");
>> - map[j].handle = BLKBACK_INVALID_HANDLE;
>> + pending_handle(pending_req, i) =
>> + BLKBACK_INVALID_HANDLE;
>
> You can make that on one line. The 80 character limit is not that ... strict anymore.
> Here is what Ingo said about it:
> https://lkml.org/lkml/2012/2/3/101
OK, good to know.
>> ret |= 1;
>> - if (persistent_gnts[i]) {
>> - rb_erase(&persistent_gnts[i]->node,
>> - &blkif->persistent_gnts);
>> - blkif->persistent_gnt_c--;
>> - kfree(persistent_gnts[i]);
>> - persistent_gnts[i] = NULL;
>> - }
>> + j++;
>> + continue;
>
> The old code had abit of different logic for the non-persistent error path.
> It would do:
>
> 598 if (!persistent_gnts[i] ||
> ..
> 602 if (unlikely(map[j].status != 0)) {
>
> 605 ret |= 1;
> .. then later.. for the !persisten_gnts case:
>
> 634 } else {
> 635 pending_handle(pending_req, i) = map[j].handle;
> 636 bitmap_set(pending_req->unmap_seg, i, 1);
> 637
> 638 if (ret) {
> 639 j++;
> 640 continue;
> 641 }
>> }
>> + pending_handle(pending_req, i) = map[j].handle;
>
> Which means that for this code, we skip the 635 (which is OK as you have done the
> "pending_handle(pending_req, i) = BLKBACK_INVALID_HANDLE", but what the 636 case
> (that is the bitmap_set)?
That's done in line 678:
678 bitmap_set(pending_req->unmap_seg, i, 1);
that is only reached if the grant is not mapped persistently. If the
grant is not mapped at all (so pending_handle ==
BLKBACK_INVALID_HANDLE), it doesn't really matter to set unmap_seg bit,
since we cannot unmap the grant.
>
> It presumarily is OK, as the 'pending_handle(pending_req, i)' ends up being
> set to BLKBACK_INVALID_HANDLE, so the loop in xen_blkbk_unmap will still skip
> over it?
>
> This I think warrants a little comment saying: "We can skip the bitmap_set' as
> xen_blkbk_unmap can handle BLKBACK_INVALID_HANDLE'.
Sure, I've added the following comment:
/*
* No need to set unmap_seg bit, since
* we can not unmap this grant because
* the handle is invalid.
*/
>
> But then that begs the question - why do we even need the bitmap_set code path anymore?
To know which grants are mapped persistenly, so we don't unmap them in
xen_blkbk_unmap.
>> }
>> - if (persistent_gnts[i]) {
>> - if (persistent_gnts[i]->handle ==
>> - BLKBACK_INVALID_HANDLE) {
>> + if (persistent_gnts[i])
>> + goto next;
>> + if (use_persistent_gnts &&
>> + blkif->persistent_gnt_c <
>> + max_mapped_grant_pages(blkif->blk_protocol)) {
>> + /*
>> + * We are using persistent grants, the grant is
>> + * not mapped but we have room for it
>> + */
>> + persistent_gnt = kmalloc(sizeof(struct persistent_gnt),
>> + GFP_KERNEL);
>> + if (!persistent_gnt) {
>> /*
>> - * If this is a new persistent grant
>> - * save the handler
>> + * If we don't have enough memory to
>> + * allocate the persistent_gnt struct
>> + * map this grant non-persistenly
>> */
>> - persistent_gnts[i]->handle = map[j++].handle;
>> + j++;
>> + goto next;
>
> So you are doing this by assuming that get_persistent_gnt in the earlier loop
> failed, which means you have in effect done this:
> map[segs_to_map++]
>
> Doing the next label will set:
> seg[i].offset = (req->u.rw.seg[i].first_sect << 9);
>
> OK, that sounds right. Is this then:
>
> bitmap_set(pending_req->unmap_seg, i, 1);
>
> even needed? The "pending_handle(pending_req, i) = map[j].handle;" had already been
> done in the /* This is a newly mapped grant */ if case, so we are set there.
We need to mark this grant as non-persistent, so we unmap it on
xen_blkbk_unmap.
>
> Perhaps you could update the comment from saying 'map this grant' (which
> implies doing it NOW as opposed to have done it already), and say:
>
> /*
> .. continue using the grant non-persistently. Note that
> we mapped it in the earlier loop and the earlier if conditional
> sets pending_handle(pending_req, i) = map[j].handle.
> */
>
>
>
>> }
>> - pending_handle(pending_req, i) =
>> - persistent_gnts[i]->handle;
>> -
>> - if (ret)
>> - continue;
>> - } else {
>> - pending_handle(pending_req, i) = map[j++].handle;
>> - bitmap_set(pending_req->unmap_seg, i, 1);
>> -
>> - if (ret)
>> - continue;
>> + persistent_gnt->gnt = map[j].ref;
>> + persistent_gnt->handle = map[j].handle;
>> + persistent_gnt->page = pages[i];
>
> Oh boy, that is a confusing. i and j. Keep loosing track which one is which.
> It lookis right.
>
>> + if (add_persistent_gnt(&blkif->persistent_gnts,
>> + persistent_gnt)) {
>> + kfree(persistent_gnt);
>
> I would also say 'persisten_gnt = NULL' for extra measure of safety
Done.
>
>
>> + j++;
>
> Perhaps the 'j' variable can be called 'map_idx' ? By this point I am pretty
> sure I know what the 'i' and 'j' variables are used for, but if somebody new
> is trying to grok this code they might spend some 5 minutes trying to figure
> this out.
Yes, I agree that i and j are not the best names, I propose to call j
new_map_idx, and i seg_idx.
>
>> + goto next;
>> + }
>> + blkif->persistent_gnt_c++;
>> + pr_debug(DRV_PFX " grant %u added to the tree of persistent grants, using %u/%u\n",
>> + persistent_gnt->gnt, blkif->persistent_gnt_c,
>> + max_mapped_grant_pages(blkif->blk_protocol));
>> + j++;
>> + goto next;
>> }
>> + if (use_persistent_gnts && !blkif->vbd.overflow_max_grants) {
>> + blkif->vbd.overflow_max_grants = 1;
>> + pr_debug(DRV_PFX " domain %u, device %#x is using maximum number of persistent grants\n",
>> + blkif->domid, blkif->vbd.handle);
>> + }
>> + bitmap_set(pending_req->unmap_seg, i, 1);
>> + j++;
>> +next:
>> seg[i].offset = (req->u.rw.seg[i].first_sect << 9);
>> }
>> return ret;
>> +
>> +out_of_memory:
>> + pr_alert(DRV_PFX "%s: out of memory\n", __func__);
>> + put_free_pages(blkif, pages_to_gnt, segs_to_map);
>> + return -ENOMEM;
>> }
>>
>> static int dispatch_discard_io(struct xen_blkif *blkif,
>> @@ -863,7 +911,7 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
>> int operation;
>> struct blk_plug plug;
>> bool drain = false;
>> - struct page *pages[BLKIF_MAX_SEGMENTS_PER_REQUEST];
>> + struct page **pages = pending_req->pages;
>>
>> switch (req->operation) {
>> case BLKIF_OP_READ:
>> @@ -1090,22 +1138,14 @@ static int __init xen_blkif_init(void)
>> xen_blkif_reqs, GFP_KERNEL);
>> blkbk->pending_grant_handles = kmalloc(sizeof(blkbk->pending_grant_handles[0]) *
>> mmap_pages, GFP_KERNEL);
>> - blkbk->pending_pages = kzalloc(sizeof(blkbk->pending_pages[0]) *
>> - mmap_pages, GFP_KERNEL);
>>
>> - if (!blkbk->pending_reqs || !blkbk->pending_grant_handles ||
>> - !blkbk->pending_pages) {
>> + if (!blkbk->pending_reqs || !blkbk->pending_grant_handles) {
>> rc = -ENOMEM;
>> goto out_of_memory;
>> }
>>
>> for (i = 0; i < mmap_pages; i++) {
>> blkbk->pending_grant_handles[i] = BLKBACK_INVALID_HANDLE;
>> - blkbk->pending_pages[i] = alloc_page(GFP_KERNEL);
>> - if (blkbk->pending_pages[i] == NULL) {
>> - rc = -ENOMEM;
>> - goto out_of_memory;
>> - }
>> }
>> rc = xen_blkif_interface_init();
>> if (rc)
>> @@ -1130,13 +1170,6 @@ static int __init xen_blkif_init(void)
>> failed_init:
>> kfree(blkbk->pending_reqs);
>> kfree(blkbk->pending_grant_handles);
>> - if (blkbk->pending_pages) {
>> - for (i = 0; i < mmap_pages; i++) {
>> - if (blkbk->pending_pages[i])
>> - __free_page(blkbk->pending_pages[i]);
>> - }
>> - kfree(blkbk->pending_pages);
>> - }
>> kfree(blkbk);
>> blkbk = NULL;
>> return rc;
>> diff --git a/drivers/block/xen-blkback/common.h b/drivers/block/xen-blkback/common.h
>> index 60103e2..6c73c38 100644
>> --- a/drivers/block/xen-blkback/common.h
>> +++ b/drivers/block/xen-blkback/common.h
>> @@ -220,6 +220,11 @@ struct xen_blkif {
>> struct rb_root persistent_gnts;
>> unsigned int persistent_gnt_c;
>>
>> + /* buffer of free pages to map grant refs */
>> + spinlock_t free_pages_lock;
>> + int free_pages_num;
>> + struct list_head free_pages;
>> +
>> /* statistics */
>> unsigned long st_print;
>> unsigned long long st_rd_req;
>> diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
>> index 8bfd1bc..24f7f6d 100644
>> --- a/drivers/block/xen-blkback/xenbus.c
>> +++ b/drivers/block/xen-blkback/xenbus.c
>> @@ -118,6 +118,9 @@ static struct xen_blkif *xen_blkif_alloc(domid_t domid)
>> blkif->st_print = jiffies;
>> init_waitqueue_head(&blkif->waiting_to_free);
>> blkif->persistent_gnts.rb_node = NULL;
>> + spin_lock_init(&blkif->free_pages_lock);
>> + INIT_LIST_HEAD(&blkif->free_pages);
>> + blkif->free_pages_num = 0;
>>
>> return blkif;
>> }
>> --
>> 1.7.7.5 (Apple Git-26)
>>
--
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