mm, memcg: use consistent gfp flags during readahead

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.

[akpm@linux-foundation.org: coding-style fixes]
[mhocko@suse.com: restrict gfp mask in mpage_alloc]
  Link: http://lkml.kernel.org/r/20160610074223.GC32285@dhcp22.suse.cz
Link: http://lkml.kernel.org/r/1465301556-26431-1-git-send-email-mhocko@kernel.org
Signed-off-by: Michal Hocko <mhocko@suse.com>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Cc: Chris Mason <clm@fb.com>
Cc: Steve French <sfrench@samba.org>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Jan Kara <jack@suse.cz>
Cc: Mike Marshall <hubcap@omnibond.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Changman Lee <cm224.lee@samsung.com>
Cc: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

8 files changed, 19 insertions, 16 deletions

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 75533adef998..e91d55837dd2 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -4180,7 +4180,8 @@ 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 d4890b6dc22d..579e41b350a2 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -3366,7 +3366,7 @@ 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 9a8bbc1fb1fa..c80dda4bdff8 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -996,7 +996,8 @@ 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..c8a05901a37b 100644
--- a/fs/mpage.c
+++ b/fs/mpage.c
@@ -71,6 +71,8 @@ mpage_alloc(struct block_device *bdev,
 {
         struct bio *bio;
 
+        /* Restrict the given (page cache) mask for slab allocations */
+        gfp_flags &= GFP_KERNEL;
         bio = bio_alloc(gfp_flags, nr_vecs);
 
         if (bio == NULL && (current->flags & PF_MEMALLOC)) {
@@ -362,7 +364,7 @@ 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..65ec288dc057 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 int nr_pages, gfp_t gfp)
 {
         struct blk_plug plug;
         unsigned page_idx;
@@ -126,10 +126,8 @@ 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))
                         mapping->a_ops->readpage(filp, page);
-                }
                 put_page(page);
         }
         ret = 0;
@@ -159,6 +157,7 @@ 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 +179,7 @@ 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 +195,7 @@ 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;