[Xen-devel] [PATCH] Dump flush write performance

Ben Guthro
Wed, 24 Oct 2007 21:10:23 -0000

Two changes to avoid disk driver using up kernel memory and triggering
oom-killer
while creating guest dump to a disk file:

1) Decreased write chunks from 16MB to 2MB;
2) Flush (fsync) after each 2MB write.

To make sure we don''t suffer significant write performance penalty,
each
of the
following cases have been tested several times to dump a 1GB guest to a
file on
a SAN disk:

With current code (16MB writes, sync once after all writes); ~38s
16MB writes, sync after each write: ~46s
2MB writes, sync after each write: ~49s

Sync-often costs us about 20%, smaller-write-size costs another 8%. The
total is
less than 30% and about 10 seconds more for a 1GB guest.

Signed-off-by: Ben Guthro <bguthro@virtualron.com>
Signed-off-by: Daniel Li <dli@virtualiron.com>


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