4 files changed, 181 insertions, 121 deletions

diff --git a/Documentation/ABI/stable/sysfs-bus-xen-backend b/Documentation/ABI/stable/sysfs-bus-xen-backend
index 3d5951c8bf5f..e04afe0cca99 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@oracle.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@citrix.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 f7526dbb204d..8245c6bb9539 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);
+        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);
+        }
+        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);
 
-static inline unsigned long vaddr(struct pending_req *req, int seg)
+        return 0;
+}
+
+static inline void put_free_pages(struct xen_blkif *blkif, struct page **page,
+                                  int num)
 {
-        unsigned long pfn = page_to_pfn(blkbk->pending_page(req, seg));
-        return (unsigned long)pfn_to_kaddr(pfn);
+        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 void shrink_free_pagepool(struct xen_blkif *blkif, int num)
+{
+        /* Remove requested pages in batches of NUM_BATCH_FREE_PAGES */
+        struct page *page[NUM_BATCH_FREE_PAGES];
+        unsigned int num_pages = 0;
+        unsigned long flags;
+
+        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 +493,19 @@ int xen_blkif_schedule(void *arg)
                 if (do_block_io_op(blkif))
                         blkif->waiting_reqs = 1;
 
+                /* Shrink if we have more than xen_blkif_max_buffer_pages */
+                shrink_free_pagepool(blkif, xen_blkif_max_buffer_pages);
+
                 if (log_stats && time_after(jiffies, blkif->st_print))
                         print_stats(blkif);
         }
 
+        /* Since we are shutting down remove all pages from the buffer */
+        shrink_free_pagepool(blkif, 0 /* All */);
+
         /* 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 +534,25 @@ 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,
@@ -487,8 +566,7 @@ static int xen_blkbk_map(struct blkif_request *req,
         struct persistent_gnt *persistent_gnt = NULL;
         struct xen_blkif *blkif = pending_req->blkif;
         phys_addr_t addr = 0;
-        int i, j;
-        bool new_map;
+        int i, seg_idx, new_map_idx;
         int nseg = req->u.rw.nr_segments;
         int segs_to_map = 0;
         int ret = 0;
@@ -517,68 +595,16 @@ 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) {
                         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,
@@ -598,48 +624,81 @@ static int xen_blkbk_map(struct blkif_request *req,
          * the page from the other domain.
          */
         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) {
+        for (seg_idx = 0, new_map_idx = 0; seg_idx < nseg; seg_idx++) {
+                if (!persistent_gnts[seg_idx]) {
                         /* This is a newly mapped grant */
-                        BUG_ON(j >= segs_to_map);
-                        if (unlikely(map[j].status != 0)) {
+                        BUG_ON(new_map_idx >= segs_to_map);
+                        if (unlikely(map[new_map_idx].status != 0)) {
                                 pr_debug(DRV_PFX "invalid buffer -- could not remap it\n");
-                                map[j].handle = BLKBACK_INVALID_HANDLE;
+                                pending_handle(pending_req, seg_idx) = BLKBACK_INVALID_HANDLE;
                                 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;
-                                }
+                                new_map_idx++;
+                                /*
+                                 * No need to set unmap_seg bit, since
+                                 * we can not unmap this grant because
+                                 * the handle is invalid.
+                                 */
+                                continue;
                         }
+                        pending_handle(pending_req, seg_idx) = map[new_map_idx].handle;
+                } else {
+                        /* This grant is persistent and already mapped */
+                        goto next;
                 }
-                if (persistent_gnts[i]) {
-                        if (persistent_gnts[i]->handle ==
-                            BLKBACK_INVALID_HANDLE) {
+                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;
+                                goto next_unmap;
                         }
-                        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[new_map_idx].ref;
+                        persistent_gnt->handle = map[new_map_idx].handle;
+                        persistent_gnt->page = pages[seg_idx];
+                        if (add_persistent_gnt(&blkif->persistent_gnts,
+                                               persistent_gnt)) {
+                                kfree(persistent_gnt);
+                                persistent_gnt = NULL;
+                                goto next_unmap;
+                        }
+                        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));
+                        new_map_idx++;
+                        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);
                 }
-                seg[i].offset = (req->u.rw.seg[i].first_sect << 9);
+next_unmap:
+                /*
+                 * We could not map this grant persistently, so use it as
+                 * a non-persistent grant.
+                 */
+                bitmap_set(pending_req->unmap_seg, seg_idx, 1);
+                new_map_idx++;
+next:
+                seg[seg_idx].offset = (req->u.rw.seg[seg_idx].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 +922,7 @@ 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 +1149,14 @@ 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 +1181,6 @@ 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 60103e2517ba..6c73c3855e65 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 8bfd1bcf95ec..24f7f6d87717 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;
 }