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authorHugh Dickins <hughd@google.com>2012-05-29 15:06:38 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-05-29 16:22:22 -0700
commitbde05d1ccd512696b09db9dd2e5f33ad19152605 (patch)
treeaffa2c836136cac6ec0e503ce8996670d385ebbb /mm/shmem.c
parent5ceb9ce6fe9462a298bb2cd5c9f1ca6cb80a0199 (diff)
shmem: replace page if mapping excludes its zone
The GMA500 GPU driver uses GEM shmem objects, but with a new twist: the backing RAM has to be below 4GB. Not a problem while the boards supported only 4GB: but now Intel's D2700MUD boards support 8GB, and their GMA3600 is managed by the GMA500 driver. shmem/tmpfs has never pretended to support hardware restrictions on the backing memory, but it might have appeared to do so before v3.1, and even now it works fine until a page is swapped out then back in. When read_cache_page_gfp() supplied a freshly allocated page for copy, that compensated for whatever choice might have been made by earlier swapin readahead; but swapoff was likely to destroy the illusion. We'd like to continue to support GMA500, so now add a new shmem_should_replace_page() check on the zone when about to move a page from swapcache to filecache (in swapin and swapoff cases), with shmem_replace_page() to allocate and substitute a suitable page (given gma500/gem.c's mapping_set_gfp_mask GFP_KERNEL | __GFP_DMA32). This does involve a minor extension to mem_cgroup_replace_page_cache() (the page may or may not have already been charged); and I've removed a comment and call to mem_cgroup_uncharge_cache_page(), which in fact is always a no-op while PageSwapCache. Also removed optimization of an unlikely path in shmem_getpage_gfp(), now that we need to check PageSwapCache more carefully (a racing caller might already have made the copy). And at one point shmem_unuse_inode() needs to use the hitherto private page_swapcount(), to guard against racing with inode eviction. It would make sense to extend shmem_should_replace_page(), to cover cpuset and NUMA mempolicy restrictions too, but set that aside for now: needs a cleanup of shmem mempolicy handling, and more testing, and ought to handle swap faults in do_swap_page() as well as shmem. Signed-off-by: Hugh Dickins <hughd@google.com> Cc: Christoph Hellwig <hch@infradead.org> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Alan Cox <alan@lxorguk.ukuu.org.uk> Cc: Stephane Marchesin <marcheu@chromium.org> Cc: Andi Kleen <andi@firstfloor.org> Cc: Dave Airlie <airlied@gmail.com> Cc: Daniel Vetter <daniel@ffwll.ch> Cc: Rob Clark <rob.clark@linaro.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/shmem.c')
-rw-r--r--mm/shmem.c141
1 files changed, 122 insertions, 19 deletions
diff --git a/mm/shmem.c b/mm/shmem.c
index be5af34a070..db72d8e44ec 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -103,6 +103,9 @@ static unsigned long shmem_default_max_inodes(void)
}
#endif
+static bool shmem_should_replace_page(struct page *page, gfp_t gfp);
+static int shmem_replace_page(struct page **pagep, gfp_t gfp,
+ struct shmem_inode_info *info, pgoff_t index);
static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
struct page **pagep, enum sgp_type sgp, gfp_t gfp, int *fault_type);
@@ -604,12 +607,13 @@ static void shmem_evict_inode(struct inode *inode)
* If swap found in inode, free it and move page from swapcache to filecache.
*/
static int shmem_unuse_inode(struct shmem_inode_info *info,
- swp_entry_t swap, struct page *page)
+ swp_entry_t swap, struct page **pagep)
{
struct address_space *mapping = info->vfs_inode.i_mapping;
void *radswap;
pgoff_t index;
- int error;
+ gfp_t gfp;
+ int error = 0;
radswap = swp_to_radix_entry(swap);
index = radix_tree_locate_item(&mapping->page_tree, radswap);
@@ -625,22 +629,37 @@ static int shmem_unuse_inode(struct shmem_inode_info *info,
if (shmem_swaplist.next != &info->swaplist)
list_move_tail(&shmem_swaplist, &info->swaplist);
+ gfp = mapping_gfp_mask(mapping);
+ if (shmem_should_replace_page(*pagep, gfp)) {
+ mutex_unlock(&shmem_swaplist_mutex);
+ error = shmem_replace_page(pagep, gfp, info, index);
+ mutex_lock(&shmem_swaplist_mutex);
+ /*
+ * We needed to drop mutex to make that restrictive page
+ * allocation; but the inode might already be freed by now,
+ * and we cannot refer to inode or mapping or info to check.
+ * However, we do hold page lock on the PageSwapCache page,
+ * so can check if that still has our reference remaining.
+ */
+ if (!page_swapcount(*pagep))
+ error = -ENOENT;
+ }
+
/*
* We rely on shmem_swaplist_mutex, not only to protect the swaplist,
* but also to hold up shmem_evict_inode(): so inode cannot be freed
* beneath us (pagelock doesn't help until the page is in pagecache).
*/
- error = shmem_add_to_page_cache(page, mapping, index,
+ if (!error)
+ error = shmem_add_to_page_cache(*pagep, mapping, index,
GFP_NOWAIT, radswap);
- /* which does mem_cgroup_uncharge_cache_page on error */
-
if (error != -ENOMEM) {
/*
* Truncation and eviction use free_swap_and_cache(), which
* only does trylock page: if we raced, best clean up here.
*/
- delete_from_swap_cache(page);
- set_page_dirty(page);
+ delete_from_swap_cache(*pagep);
+ set_page_dirty(*pagep);
if (!error) {
spin_lock(&info->lock);
info->swapped--;
@@ -660,7 +679,14 @@ int shmem_unuse(swp_entry_t swap, struct page *page)
struct list_head *this, *next;
struct shmem_inode_info *info;
int found = 0;
- int error;
+ int error = 0;
+
+ /*
+ * There's a faint possibility that swap page was replaced before
+ * caller locked it: it will come back later with the right page.
+ */
+ if (unlikely(!PageSwapCache(page)))
+ goto out;
/*
* Charge page using GFP_KERNEL while we can wait, before taking
@@ -676,7 +702,7 @@ int shmem_unuse(swp_entry_t swap, struct page *page)
list_for_each_safe(this, next, &shmem_swaplist) {
info = list_entry(this, struct shmem_inode_info, swaplist);
if (info->swapped)
- found = shmem_unuse_inode(info, swap, page);
+ found = shmem_unuse_inode(info, swap, &page);
else
list_del_init(&info->swaplist);
cond_resched();
@@ -685,8 +711,6 @@ int shmem_unuse(swp_entry_t swap, struct page *page)
}
mutex_unlock(&shmem_swaplist_mutex);
- if (!found)
- mem_cgroup_uncharge_cache_page(page);
if (found < 0)
error = found;
out:
@@ -856,6 +880,84 @@ static inline struct mempolicy *shmem_get_sbmpol(struct shmem_sb_info *sbinfo)
#endif
/*
+ * When a page is moved from swapcache to shmem filecache (either by the
+ * usual swapin of shmem_getpage_gfp(), or by the less common swapoff of
+ * shmem_unuse_inode()), it may have been read in earlier from swap, in
+ * ignorance of the mapping it belongs to. If that mapping has special
+ * constraints (like the gma500 GEM driver, which requires RAM below 4GB),
+ * we may need to copy to a suitable page before moving to filecache.
+ *
+ * In a future release, this may well be extended to respect cpuset and
+ * NUMA mempolicy, and applied also to anonymous pages in do_swap_page();
+ * but for now it is a simple matter of zone.
+ */
+static bool shmem_should_replace_page(struct page *page, gfp_t gfp)
+{
+ return page_zonenum(page) > gfp_zone(gfp);
+}
+
+static int shmem_replace_page(struct page **pagep, gfp_t gfp,
+ struct shmem_inode_info *info, pgoff_t index)
+{
+ struct page *oldpage, *newpage;
+ struct address_space *swap_mapping;
+ pgoff_t swap_index;
+ int error;
+
+ oldpage = *pagep;
+ swap_index = page_private(oldpage);
+ swap_mapping = page_mapping(oldpage);
+
+ /*
+ * We have arrived here because our zones are constrained, so don't
+ * limit chance of success by further cpuset and node constraints.
+ */
+ gfp &= ~GFP_CONSTRAINT_MASK;
+ newpage = shmem_alloc_page(gfp, info, index);
+ if (!newpage)
+ return -ENOMEM;
+ VM_BUG_ON(shmem_should_replace_page(newpage, gfp));
+
+ *pagep = newpage;
+ page_cache_get(newpage);
+ copy_highpage(newpage, oldpage);
+
+ VM_BUG_ON(!PageLocked(oldpage));
+ __set_page_locked(newpage);
+ VM_BUG_ON(!PageUptodate(oldpage));
+ SetPageUptodate(newpage);
+ VM_BUG_ON(!PageSwapBacked(oldpage));
+ SetPageSwapBacked(newpage);
+ VM_BUG_ON(!swap_index);
+ set_page_private(newpage, swap_index);
+ VM_BUG_ON(!PageSwapCache(oldpage));
+ SetPageSwapCache(newpage);
+
+ /*
+ * Our caller will very soon move newpage out of swapcache, but it's
+ * a nice clean interface for us to replace oldpage by newpage there.
+ */
+ spin_lock_irq(&swap_mapping->tree_lock);
+ error = shmem_radix_tree_replace(swap_mapping, swap_index, oldpage,
+ newpage);
+ __inc_zone_page_state(newpage, NR_FILE_PAGES);
+ __dec_zone_page_state(oldpage, NR_FILE_PAGES);
+ spin_unlock_irq(&swap_mapping->tree_lock);
+ BUG_ON(error);
+
+ mem_cgroup_replace_page_cache(oldpage, newpage);
+ lru_cache_add_anon(newpage);
+
+ ClearPageSwapCache(oldpage);
+ set_page_private(oldpage, 0);
+
+ unlock_page(oldpage);
+ page_cache_release(oldpage);
+ page_cache_release(oldpage);
+ return 0;
+}
+
+/*
* shmem_getpage_gfp - find page in cache, or get from swap, or allocate
*
* If we allocate a new one we do not mark it dirty. That's up to the
@@ -923,19 +1025,20 @@ repeat:
/* We have to do this with page locked to prevent races */
lock_page(page);
+ if (!PageSwapCache(page) || page->mapping) {
+ error = -EEXIST; /* try again */
+ goto failed;
+ }
if (!PageUptodate(page)) {
error = -EIO;
goto failed;
}
wait_on_page_writeback(page);
- /* Someone may have already done it for us */
- if (page->mapping) {
- if (page->mapping == mapping &&
- page->index == index)
- goto done;
- error = -EEXIST;
- goto failed;
+ if (shmem_should_replace_page(page, gfp)) {
+ error = shmem_replace_page(&page, gfp, info, index);
+ if (error)
+ goto failed;
}
error = mem_cgroup_cache_charge(page, current->mm,
@@ -998,7 +1101,7 @@ repeat:
if (sgp == SGP_DIRTY)
set_page_dirty(page);
}
-done:
+
/* Perhaps the file has been truncated since we checked */
if (sgp != SGP_WRITE &&
((loff_t)index << PAGE_CACHE_SHIFT) >= i_size_read(inode)) {