The patch titled
Subject: epoll: comment + BUILD_BUG_ON to prevent epitem bloat
has been added to the -mm tree. Its filename is
epoll-trim-epitem-by-one-cache-line-on-x86_64-fix-fix.patch
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------------------------------------------------------
From: Eric Wong <normalperson@xxxxxxxx>
Subject: epoll: comment + BUILD_BUG_ON to prevent epitem bloat
This will prevent us from accidentally introducing a memory bloat
regression here in the future.
Signed-off-by: Eric Wong <normalperson@xxxxxxxx>
Cc: Davide Libenzi <davidel@xxxxxxxxxxxxxxx>,
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/eventpoll.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff -puN fs/eventpoll.c~epoll-trim-epitem-by-one-cache-line-on-x86_64-fix-fix fs/eventpoll.c
--- a/fs/eventpoll.c~epoll-trim-epitem-by-one-cache-line-on-x86_64-fix-fix
+++ a/fs/eventpoll.c
@@ -129,6 +129,8 @@ struct nested_calls {
/*
* Each file descriptor added to the eventpoll interface will
* have an entry of this type linked to the "rbr" RB tree.
+ * Avoid increasing the size of this struct, there can be many thousands
+ * of these on a server and we do not want this to take another cache line.
*/
struct epitem {
/* RB tree node used to link this structure to the eventpoll RB tree */
@@ -2011,6 +2013,12 @@ static int __init eventpoll_init(void)
/* Initialize the structure used to perform file's f_op->poll() calls */
ep_nested_calls_init(&poll_readywalk_ncalls);
+ /*
+ * We can have many thousands of epitems, so prevent this from
+ * using an extra cache line on 64-bit (and smaller) CPUs
+ */
+ BUILD_BUG_ON(sizeof(void *) <= 8 && sizeof(struct epitem) > 128);
+
/* Allocates slab cache used to allocate "struct epitem" items */
epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem),
0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
_
Patches currently in -mm which might be from normalperson@xxxxxxxx are
epoll-trim-epitem-by-one-cache-line-on-x86_64.patch
epoll-trim-epitem-by-one-cache-line-on-x86_64-fix.patch
epoll-trim-epitem-by-one-cache-line-on-x86_64-fix-fix.patch
epoll-use-rcu-to-protect-wakeup_source-in-epitem.patch
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