From: Michal Hocko <mhocko@xxxxxxxx>
Vladimir has noticed that we might declare memcg oom even during
readahead because read_pages only uses GFP_KERNEL (with mapping_gfp
restriction) while __do_page_cache_readahead uses
page_cache_alloc_readahead which adds __GFP_NORETRY to prevent from
OOMs. This gfp mask discrepancy is really unfortunate and easily
fixable. Drop page_cache_alloc_readahead() which only has one user
and outsource the gfp_mask logic into readahead_gfp_mask and propagate
this mask from __do_page_cache_readahead down to read_pages.
This alone would have only very limited impact as most filesystems
are implementing ->readpages and the common implementation
mpage_readpages does GFP_KERNEL (with mapping_gfp restriction) again.
We can tell it to use readahead_gfp_mask instead as this function is
called only during readahead as well. The same applies to
read_cache_pages.
ext4 has its own ext4_mpage_readpages but the path which has pages !=
NULL can use the same gfp mask.
Btrfs, cifs, f2fs and orangefs are doing a very similar pattern to
mpage_readpages so the same can be applied to them as well.
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
---
Hi,
an alternative solution for ->readpages part would be add the gfp mask
as a new argument. This would be a larger change and I am not even sure
it would be so much better. An explicit usage of the readahead gfp mask
sounds like easier to track. If there is a general agreement this is a
proper way to go I can rework the patch to do so, of course.
Does this make sense?
fs/btrfs/extent_io.c | 3 ++-
fs/cifs/file.c | 2 +-
fs/ext4/readpage.c | 2 +-
fs/f2fs/data.c | 3 ++-
fs/mpage.c | 2 +-
fs/orangefs/inode.c | 2 +-
include/linux/pagemap.h | 6 +++---
mm/readahead.c | 12 ++++++------
8 files changed, 17 insertions(+), 15 deletions(-)
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index d247fc0eea19..883031d9f35b 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -4160,7 +4160,8 @@ int extent_readpages(struct extent_io_tree *tree,
prefetchw(&page->flags);
list_del(&page->lru);
if (add_to_page_cache_lru(page, mapping,
- page->index, GFP_NOFS)) {
+ page->index,
+ readahead_gfp_mask(mapping))) {
put_page(page);
continue;
}
diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index c03d0744648b..60e0167b0c1d 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -3380,7 +3380,7 @@ readpages_get_pages(struct address_space *mapping, struct list_head *page_list,
struct page *page, *tpage;
unsigned int expected_index;
int rc;
- gfp_t gfp = mapping_gfp_constraint(mapping, GFP_KERNEL);
+ gfp_t gfp = readahead_gfp_mask(mapping);
INIT_LIST_HEAD(tmplist);
diff --git a/fs/ext4/readpage.c b/fs/ext4/readpage.c
index dc54a4b60eba..c75b66a64982 100644
--- a/fs/ext4/readpage.c
+++ b/fs/ext4/readpage.c
@@ -166,7 +166,7 @@ int ext4_mpage_readpages(struct address_space *mapping,
page = list_entry(pages->prev, struct page, lru);
list_del(&page->lru);
if (add_to_page_cache_lru(page, mapping, page->index,
- mapping_gfp_constraint(mapping, GFP_KERNEL)))
+ readahead_gfp_mask(mapping)))
goto next_page;
}
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 5dafb9cef12e..3f914339e4f4 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -928,7 +928,8 @@ static int f2fs_mpage_readpages(struct address_space *mapping,
page = list_entry(pages->prev, struct page, lru);
list_del(&page->lru);
if (add_to_page_cache_lru(page, mapping,
- page->index, GFP_KERNEL))
+ page->index,
+ readahead_gfp_mask(mapping)))
goto next_page;
}
diff --git a/fs/mpage.c b/fs/mpage.c
index eedc644b78d7..9c11255b0797 100644
--- a/fs/mpage.c
+++ b/fs/mpage.c
@@ -362,7 +362,7 @@ mpage_readpages(struct address_space *mapping, struct list_head *pages,
sector_t last_block_in_bio = 0;
struct buffer_head map_bh;
unsigned long first_logical_block = 0;
- gfp_t gfp = mapping_gfp_constraint(mapping, GFP_KERNEL);
+ gfp_t gfp = readahead_gfp_mask(mapping);
map_bh.b_state = 0;
map_bh.b_size = 0;
diff --git a/fs/orangefs/inode.c b/fs/orangefs/inode.c
index 85640e955cde..06a8da75651d 100644
--- a/fs/orangefs/inode.c
+++ b/fs/orangefs/inode.c
@@ -80,7 +80,7 @@ static int orangefs_readpages(struct file *file,
if (!add_to_page_cache(page,
mapping,
page->index,
- GFP_KERNEL)) {
+ readahead_gfp_mask(mapping))) {
ret = read_one_page(page);
gossip_debug(GOSSIP_INODE_DEBUG,
"failure adding page to cache, read_one_page returned: %d\n",
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 97354102794d..81363b834900 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -209,10 +209,10 @@ static inline struct page *page_cache_alloc_cold(struct address_space *x)
return __page_cache_alloc(mapping_gfp_mask(x)|__GFP_COLD);
}
-static inline struct page *page_cache_alloc_readahead(struct address_space *x)
+static inline gfp_t readahead_gfp_mask(struct address_space *x)
{
- return __page_cache_alloc(mapping_gfp_mask(x) |
- __GFP_COLD | __GFP_NORETRY | __GFP_NOWARN);
+ return mapping_gfp_mask(x) |
+ __GFP_COLD | __GFP_NORETRY | __GFP_NOWARN;
}
typedef int filler_t(void *, struct page *);
diff --git a/mm/readahead.c b/mm/readahead.c
index 40be3ae0afe3..7cd032ef17bf 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -89,7 +89,7 @@ int read_cache_pages(struct address_space *mapping, struct list_head *pages,
page = lru_to_page(pages);
list_del(&page->lru);
if (add_to_page_cache_lru(page, mapping, page->index,
- mapping_gfp_constraint(mapping, GFP_KERNEL))) {
+ readahead_gfp_mask(mapping))) {
read_cache_pages_invalidate_page(mapping, page);
continue;
}
@@ -108,7 +108,7 @@ int read_cache_pages(struct address_space *mapping, struct list_head *pages,
EXPORT_SYMBOL(read_cache_pages);
static int read_pages(struct address_space *mapping, struct file *filp,
- struct list_head *pages, unsigned nr_pages)
+ struct list_head *pages, unsigned nr_pages, gfp_t gfp_mask)
{
struct blk_plug plug;
unsigned page_idx;
@@ -126,8 +126,7 @@ static int read_pages(struct address_space *mapping, struct file *filp,
for (page_idx = 0; page_idx < nr_pages; page_idx++) {
struct page *page = lru_to_page(pages);
list_del(&page->lru);
- if (!add_to_page_cache_lru(page, mapping, page->index,
- mapping_gfp_constraint(mapping, GFP_KERNEL))) {
+ if (!add_to_page_cache_lru(page, mapping, page->index, gfp_mask)) {
mapping->a_ops->readpage(filp, page);
}
put_page(page);
@@ -159,6 +158,7 @@ int __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
int page_idx;
int ret = 0;
loff_t isize = i_size_read(inode);
+ gfp_t gfp_mask = readahead_gfp_mask(mapping);
if (isize == 0)
goto out;
@@ -180,7 +180,7 @@ int __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
if (page && !radix_tree_exceptional_entry(page))
continue;
- page = page_cache_alloc_readahead(mapping);
+ page = __page_cache_alloc(gfp_mask);
if (!page)
break;
page->index = page_offset;
@@ -196,7 +196,7 @@ int __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
* will then handle the error.
*/
if (ret)
- read_pages(mapping, filp, &page_pool, ret);
+ read_pages(mapping, filp, &page_pool, ret, gfp_mask);
BUG_ON(!list_empty(&page_pool));
out:
return ret;
--
2.8.1
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