It is common for epoll users to have thousands of epitems, so saving a
cache line on every allocation leads to large memory savings.
Since epitem allocations are cache-aligned, reducing sizeof(struct
epitem) from 136 bytes to 128 bytes will allow it to squeeze under a
cache line boundary on x86_64.
>From /sys/kernel/slab/eventpoll_epi, I see the following changes on my
x86_64 Core2 Duo (which has 64-byte cache alignment):
object_size : 192 => 128
objs_per_slab: 21 => 32
I have no access to other 64-bit machines, so I am limiting this to
x86_64-only with EPOLL_PACKED instead of __attribute__((packed))
Signed-off-by: Eric Wong <normalperson@xxxxxxxx>
Cc: Davide Libenzi <davidel@xxxxxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/eventpoll.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index cfc4b16..06f3d0e 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -107,7 +107,7 @@
struct epoll_filefd {
struct file *file;
int fd;
-};
+} EPOLL_PACKED;
/*
* Structure used to track possible nested calls, for too deep recursions
--
Eric Wong
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