Bug 146410 - [zfs] [patch] bad file copy performance from UFS to ZFS
Summary: [zfs] [patch] bad file copy performance from UFS to ZFS
Status: Open
Alias: None
Product: Base System
Classification: Unclassified
Component: kern (show other bugs)
Version: 8.0-STABLE
Hardware: Any Any
: Normal Affects Only Me
Assignee: freebsd-bugs mailing list
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2010-05-08 22:00 UTC by Juha-Matti Tilli
Modified: 2017-12-31 22:34 UTC (History)
0 users

See Also:


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Description Juha-Matti Tilli 2010-05-08 22:00:10 UTC
When copying files from UFS to ZFS, performance decreases quickly to a small
fraction of the transfer rate of disks. The problem seems to be that caching of
files on UFS decreases the available memory so much that ZFS decreases ARC size
to the minimum and starts to throttle writes.

Fix: I've managed to get better performance by modifying arc_memory_throttle to
include v_cache_count in addition to v_free_count to the number of available
pages, and increasing vm.v_cache_min and vm.v_cache_max so that more cached
file data is included in v_cache_count instead of v_inactive_count.

Here's a patch to sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c:



With this patch, vfs.zfs.arc_min=671088640, vm.v_cache_min=300000 and
vm.v_cache_max=400000, performance is adequate and I haven't seen a single
increase of kstat.zfs.misc.arcstats.memory_throttle_count.

This still doesn't solve the problem that ZFS decreases ARC size when reading
from UFS. One way to fix that would be to implement a configurable maximum
limit for the amount of cached file data for UFS, like vfs.zfs.arc_max for ZFS.

Another way to prevent ARC from decreasing is increasing vfs.zfs.arc_min when
copying data from a UFS partition and decreasing it to the original value after
all data is copied. However, vfs.zfs.arc_min can't be changed with sysctl, so
that approach requires two reboots. Perhaps it should be made possible to
change vfs.zfs.arc_min without requiring a reboot?--QMBaLa9nyItJOj4yUfKY1ZzQyj5kNnXR6a847TysjUYXQdfM
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--- arc.c.orig  2010-05-08 17:53:38.343964308 +0300
+++ arc.c       2010-05-08 17:57:34.756952644 +0300
@@ -3516,7 +3516,8 @@
 {
 #ifdef _KERNEL
        uint64_t inflight_data = arc_anon->arcs_size;
-       uint64_t available_memory = ptoa((uintmax_t)cnt.v_free_count);
+       uint64_t available_memory = ptoa((uintmax_t)cnt.v_free_count +
+                                        (uintmax_t)cnt.v_cache_count);
        static uint64_t page_load = 0;
        static uint64_t last_txg = 0;
How-To-Repeat: 
Mount a ZFS filesystem and a UFS filesystem. Copy large files from UFS to ZFS.
Wait until top(1) shows that there is little memory free and that
kstat.zfs.misc.arcstats.size has decreased to vfs.zfs.arc_min. Observe the bad
performance and the continuous rapid increase of
kstat.zfs.misc.arcstats.memory_throttle_count.
Comment 1 Mark Linimon freebsd_committer freebsd_triage 2010-05-09 23:08:29 UTC
Responsible Changed
From-To: freebsd-bugs->freebsd-fs

Over to maintainer(s).
Comment 2 Pawel Jakub Dawidek freebsd_committer 2010-05-10 11:03:51 UTC
Responsible Changed
From-To: freebsd-fs->pjd

I'll take this one.
Comment 3 dfilter service freebsd_committer 2010-09-17 08:14:15 UTC
Author: avg
Date: Fri Sep 17 07:14:07 2010
New Revision: 212780
URL: http://svn.freebsd.org/changeset/base/212780

Log:
  zfs arc_reclaim_needed: more reasonable threshold for available pages
  
  vm_paging_target() is not a trigger of any kind for pageademon, but
  rather a "soft" target for it when it's already triggered.
  Thus, trying to keep 2048 pages above that level at the expense of ARC
  was simply driving ARC size into the ground even with normal memory
  loads.
  Instead, use a threshold at which a pagedaemon scan is triggered, so
  that ARC reclaiming helps with pagedaemon's task, but the latter still
  recycles active and inactive pages.
  
  PR:		kern/146410, kern/138790
  MFC after:	3 weeks

Modified:
  head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c

Modified: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c
==============================================================================
--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c	Fri Sep 17 04:55:01 2010	(r212779)
+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c	Fri Sep 17 07:14:07 2010	(r212780)
@@ -2161,10 +2161,10 @@ arc_reclaim_needed(void)
 		return (0);
 
 	/*
-	 * If pages are needed or we're within 2048 pages
-	 * of needing to page need to reclaim
+	 * Cooperate with pagedaemon when it's time for it to scan
+	 * and reclaim some pages.
 	 */
-	if (vm_pages_needed || (vm_paging_target() > -2048))
+	if (vm_paging_need())
 		return (1);
 
 #if 0
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Comment 4 dfilter service freebsd_committer 2010-09-17 08:34:57 UTC
Author: avg
Date: Fri Sep 17 07:34:50 2010
New Revision: 212783
URL: http://svn.freebsd.org/changeset/base/212783

Log:
  zfs arc_reclaim_needed: fix typo in mismerge in r212780
  
  PR:		kern/146410, kern/138790
  MFC after:	3 weeks
  X-MFC with:	r212780

Modified:
  head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c

Modified: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c
==============================================================================
--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c	Fri Sep 17 07:20:20 2010	(r212782)
+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c	Fri Sep 17 07:34:50 2010	(r212783)
@@ -2160,7 +2160,7 @@ arc_reclaim_needed(void)
 	 * Cooperate with pagedaemon when it's time for it to scan
 	 * and reclaim some pages.
 	 */
-	if (vm_paging_need())
+	if (vm_paging_needed())
 		return (1);
 
 #if 0
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Comment 5 chris 2011-02-08 17:15:34 UTC
Hi is there any progress on this?

Am using 8.2-RC3 and FreeBSD has the exact same problem many months later.

I was reading from UFS backups and my ufs cache using over 7 gig of ram in a
12gig machine rampant usage unchecked and zfs reducing its cache to make
room.

Really I agree with the original reporter that zfs tunables shouldnt need a
reboot and more importantly ufs needs a sysctl knob to throttle its cache.

I am considering setting a min cache size for zfs but I fear that ufs still
wont hold back and I will find many gigs of memory swapped out.
Comment 6 Eitan Adler freebsd_committer freebsd_triage 2017-12-31 07:59:38 UTC
For bugs matching the following criteria:

Status: In Progress Changed: (is less than) 2014-06-01

Reset to default assignee and clear in-progress tags.

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