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osdc/ObjectCacher: limit writeback IOs generated while holding lock

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While analyzing a log from Mike Dawson I saw a long stall while librbd's
objectcacher was starting lots (many hundreds) of IOs.  Limit the amount of
time we spend doing this at a time to allow IO replies to be processed so
that the cache remains responsive.

I'm not sure this warrants a tunable (which we would need to add for both
libcephfs and librbd).

Signed-off-by: Sage Weil <sage@inktank.com>
This commit is contained in:
Sage Weil 2013-10-01 09:28:29 -07:00
parent 055e31359a
commit cce990efc8
1 changed files with 5 additions and 1 deletions
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6
src/osdc/ObjectCacher.cc
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@ -11,6 +11,8 @@
#include "include/assert.h" #include "include/assert.h"
#define MAX_FLUSH_UNDER_LOCK 20 ///< max bh's we start writeback on while holding the lock
/*** ObjectCacher::BufferHead ***/ /*** ObjectCacher::BufferHead ***/
@ -1448,8 +1450,10 @@ void ObjectCacher::flusher_entry()
utime_t cutoff = ceph_clock_now(cct); utime_t cutoff = ceph_clock_now(cct);
cutoff -= max_dirty_age; cutoff -= max_dirty_age;
BufferHead *bh = 0; BufferHead *bh = 0;
int max = MAX_FLUSH_UNDER_LOCK;
while ((bh = static_cast<BufferHead*>(bh_lru_dirty.lru_get_next_expire())) != 0 && while ((bh = static_cast<BufferHead*>(bh_lru_dirty.lru_get_next_expire())) != 0 &&
bh->last_write < cutoff) { bh->last_write < cutoff &&
--max > 0) {
ldout(cct, 10) << "flusher flushing aged dirty bh " << *bh << dendl; ldout(cct, 10) << "flusher flushing aged dirty bh " << *bh << dendl;
bh_write(bh); bh_write(bh);
} }