path: root/mm
diff options
authorShakeel Butt <shakeelb@google.com>2017-09-08 16:13:05 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-09-08 18:26:47 -0700
commit3a77d214807c32f900618cee0432feb4f7f99c65 (patch)
tree8a65f4ea44501b1993dc55fdc8043e0dffaedbcc /mm
parent3eb95feac113d8ebad5b7b5189a65efcbd95a749 (diff)
mm: fadvise: avoid fadvise for fs without backing device
The fadvise() manpage is silent on fadvise()'s effect on memory-based filesystems (shmem, hugetlbfs & ramfs) and pseudo file systems (procfs, sysfs, kernfs). The current implementaion of fadvise is mostly a noop for such filesystems except for FADV_DONTNEED which will trigger expensive remote LRU cache draining. This patch makes the noop of fadvise() on such file systems very explicit. However this change has two side effects for ramfs and one for tmpfs. First fadvise(FADV_DONTNEED) could remove the unmapped clean zero'ed pages of ramfs (allocated through read, readahead & read fault) and tmpfs (allocated through read fault). Also fadvise(FADV_WILLNEED) could create such clean zero'ed pages for ramfs. This change removes those possibilities. One of our generic libraries does fadvise(FADV_DONTNEED). Recently we observed high latency in fadvise() and noticed that the users have started using tmpfs files and the latency was due to expensive remote LRU cache draining. For normal tmpfs files (have data written on them), fadvise(FADV_DONTNEED) will always trigger the unneeded remote cache draining. Link: http://lkml.kernel.org/r/20170818011023.181465-1-shakeelb@google.com Signed-off-by: Shakeel Butt <shakeelb@google.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Hillf Danton <hillf.zj@alibaba-inc.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Hugh Dickins <hughd@google.com> Cc: Greg Thelen <gthelen@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
1 files changed, 3 insertions, 3 deletions
diff --git a/mm/fadvise.c b/mm/fadvise.c
index a43013112581..702f239cd6db 100644
--- a/mm/fadvise.c
+++ b/mm/fadvise.c
@@ -52,7 +52,9 @@ SYSCALL_DEFINE4(fadvise64_64, int, fd, loff_t, offset, loff_t, len, int, advice)
goto out;
- if (IS_DAX(inode)) {
+ bdi = inode_to_bdi(mapping->host);
+ if (IS_DAX(inode) || (bdi == &noop_backing_dev_info)) {
switch (advice) {
@@ -75,8 +77,6 @@ SYSCALL_DEFINE4(fadvise64_64, int, fd, loff_t, offset, loff_t, len, int, advice)
endbyte--; /* inclusive */
- bdi = inode_to_bdi(mapping->host);
switch (advice) {
f.file->f_ra.ra_pages = bdi->ra_pages;