On Mon, Dec 05, 2016 at 09:52:36PM -0800, Hugh Dickins wrote:
> Callers of shmem_mapping() are interested in whether the mapping is
> swap backed - except for uprobes, which is interested in whether it
> should use shmem_read_mapping_page(). All these callers are better
> served by a shmem_mapping() which checks for shmem_aops, than the
> current version which goes through several indirections to find where
> the inode lives - and has the surprising effect that a private mmap of
> /dev/zero satisfies both vma_is_anonymous() and shmem_mapping(), when
> that device node is on devtmpfs. I don't think anything in the tree
> suffers from that surprise, but it caught me out, and is better fixed.
>
> Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
There are actually some existing sites that check for shmemness this
way. Do you see value in converting them?
---
>From 1f85c9c8b7ec59a804a52f497ed582615b9caed5 Mon Sep 17 00:00:00 2001
From: Johannes Weiner <hannes@xxxxxxxxxxx>
Date: Wed, 14 Dec 2016 16:07:35 -0500
Subject: [PATCH] mm: shmem: convert open-coded sites to use shmem_mapping()
Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
---
mm/shmem.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/mm/shmem.c b/mm/shmem.c
index 41537fd080b9..f1b52c337e62 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1021,7 +1021,7 @@ static void shmem_evict_inode(struct inode *inode)
struct shmem_inode_info *info = SHMEM_I(inode);
struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
- if (inode->i_mapping->a_ops == &shmem_aops) {
+ if (shmem_mapping(inode->i_mapping)) {
shmem_unacct_size(info->flags, inode->i_size);
inode->i_size = 0;
shmem_truncate_range(inode, 0, (loff_t)-1);
@@ -1671,7 +1671,7 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
} else {
/* shmem_symlink() */
- if (mapping->a_ops != &shmem_aops)
+ if (!shmem_mapping(mapping))
goto alloc_nohuge;
if (shmem_huge == SHMEM_HUGE_DENY || sgp_huge == SGP_NOHUGE)
goto alloc_nohuge;
@@ -4105,7 +4105,7 @@ struct page *shmem_read_mapping_page_gfp(struct address_space *mapping,
struct page *page;
int error;
- BUG_ON(mapping->a_ops != &shmem_aops);
+ BUG_ON(!shmem_mapping(mapping));
error = shmem_getpage_gfp(inode, index, &page, SGP_CACHE,
gfp, NULL, NULL);
if (error)
--
2.10.2
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