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Several improvements to ARC shrinking (#16197)

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- When receiving memory pressure signal from OS be more strict
trying to free some memory.  Otherwise kernel may come again and
request much more.  Return as result how much arc_c was actually
reduced due to this request, that may be less than requested.
 - On Linux when receiving direct reclaim from some file system
(that may be ZFS) instead of ignoring request completely, just
shrink the ARC, but do not wait for eviction.  Waiting there may
cause deadlock.  Ignoring it as before may put extra pressure on
other caches and/or swap, and cause OOM if nothing help.  While
not waiting may result in more ARC evicted later, and may be too
late if OOM killer activate right now, but I hope it to be better
than doing nothing at all.
 - On Linux set arc_no_grow before waiting for reclaim, not after,
or it may grow back while we are waiting.
 - On Linux add new parameter zfs_arc_shrinker_seeks to balance
ARC eviction cost, relative to page cache and other subsystems.
 - Slightly update Linux arc_set_sys_free() math for new kernels.

Signed-off-by:	Alexander Motin <mav@FreeBSD.org>
Sponsored by:	iXsystems, Inc.
Reviewed-by: Rob Norris <rob.norris@klarasystems.com>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
This commit is contained in:
Alexander Motin
2024-07-25 13:31:14 -04:00
committed by GitHub
parent c7ada64bb6
commit 55427add3c
5 changed files with 125 additions and 96 deletions
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module/os/freebsd/zfs/arc_os.c
+6 -7
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@@ -149,18 +149,17 @@ static eventhandler_tag arc_event_lowmem = NULL;
static void
arc_lowmem(void *arg __unused, int howto __unused)
{
int64_t free_memory, to_free;
int64_t can_free, free_memory, to_free;
arc_no_grow = B_TRUE;
arc_warm = B_TRUE;
arc_growtime = gethrtime() + SEC2NSEC(arc_grow_retry);
free_memory = arc_available_memory();
int64_t can_free = arc_c - arc_c_min;
if (can_free <= 0)
return;
to_free = (can_free >> arc_shrink_shift) - MIN(free_memory, 0);
can_free = arc_c - arc_c_min;
to_free = (MAX(can_free, 0) >> arc_shrink_shift) - MIN(free_memory, 0);
DTRACE_PROBE2(arc__needfree, int64_t, free_memory, int64_t, to_free);
arc_reduce_target_size(to_free);
to_free = arc_reduce_target_size(to_free);
/*
* It is unsafe to block here in arbitrary threads, because we can come
@@ -168,7 +167,7 @@ arc_lowmem(void *arg __unused, int howto __unused)
* with ARC reclaim thread.
*/
if (curproc == pageproc)
arc_wait_for_eviction(to_free, B_FALSE);
arc_wait_for_eviction(to_free, B_FALSE, B_FALSE);
}
void