From: Konstantin Khlebnikov <koct9i@gmail.com>
To: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
linux-mm@kvack.org, Alexander Viro <viro@zeniv.linux.org.uk>,
Waiman Long <longman@redhat.com>,
Gautham Ananthakrishna <gautham.ananthakrishna@oracle.com>,
matthew.wilcox@oracle.com
Subject: Re: [PATCH RFC 0/8] dcache: increase poison resistance
Date: Thu, 17 Dec 2020 18:47:16 +0300 [thread overview]
Message-ID: <CALYGNiPi+dqYgvTRwtcQXGAsdexCifJe4X7NN6tx4etrTcnyjA@mail.gmail.com> (raw)
In-Reply-To: <4bcbd2e7-b5e3-6f45-51cf-8658f9c9009d@oracle.com>
[-- Attachment #1: Type: text/plain, Size: 4346 bytes --]
On Wed, Dec 16, 2020 at 9:47 PM Junxiao Bi <junxiao.bi@oracle.com> wrote:
> Hi Konstantin,
>
> How would you like to proceed with this patch set?
>
> This patchset as it is already fixed the customer issue we faced, it
> will stop memory fragmentation causing by negative dentry and no
> performance regression through our test. In production workload, it is
> common that some app kept creating and removing tmp files, this will
> leave a lot of negative dentry over time, some time later, it will cause
> memory fragmentation and system run into memory compaction and not
> responsible. It will be good to push it to upstream merge. If you are
> busy, we can try push it again.
>
Feel free to try.
You may drop fist hunk of changes which fixes slow inotify and keep only
dances around hash chains.
Thanks,
>
> Junxiao.
>
> On 12/14/20 3:10 PM, Junxiao Bi wrote:
> > On 12/13/20 11:43 PM, Konstantin Khlebnikov wrote:
> >
> >>
> >>
> >> On Sun, Dec 13, 2020 at 9:52 PM Junxiao Bi <junxiao.bi@oracle.com
> >> <mailto:junxiao.bi@oracle.com>> wrote:
> >>
> >> On 12/11/20 11:32 PM, Konstantin Khlebnikov wrote:
> >>
> >> > On Thu, Dec 10, 2020 at 2:01 AM Junxiao Bi
> >> <junxiao.bi@oracle.com <mailto:junxiao.bi@oracle.com>
> >> > <mailto:junxiao.bi@oracle.com <mailto:junxiao.bi@oracle.com>>>
> >> wrote:
> >> >
> >> > Hi Konstantin,
> >> >
> >> > We tested this patch set recently and found it limiting
> >> negative
> >> > dentry
> >> > to a small part of total memory. And also we don't see any
> >> > performance
> >> > regression on it. Do you have any plan to integrate it into
> >> > mainline? It
> >> > will help a lot on memory fragmentation issue causing by
> >> dentry slab,
> >> > there were a lot of customer cases where sys% was very high
> >> since
> >> > most
> >> > cpu were doing memory compaction, dentry slab was taking too
> >> much
> >> > memory
> >> > and nearly all dentry there were negative.
> >> >
> >> >
> >> > Right now I don't have any plans for this. I suspect such
> >> problems will
> >> > appear much more often since machines are getting bigger.
> >> > So, somebody will take care of it.
> >> We already had a lot of customer cases. It made no sense to leave so
> >> many negative dentry in the system, it caused memory fragmentation
> >> and
> >> not much benefit.
> >>
> >>
> >> Dcache could grow so big only if the system lacks of memory pressure.
> >>
> >> Simplest solution is a cronjob which provinces such pressure by
> >> creating sparse file on disk-based fs and then reading it.
> >> This should wash away all inactive caches with no IO and zero chance
> >> of oom.
> > Sound good, will try.
> >>
> >> >
> >> > First part which collects negative dentries at the end list of
> >> > siblings could be
> >> > done in a more obvious way by splitting the list in two.
> >> > But this touches much more code.
> >> That would add new field to dentry?
> >>
> >>
> >> Yep. Decision is up to maintainers.
> >>
> >> >
> >> > Last patch isn't very rigid but does non-trivial changes.
> >> > Probably it's better to call some garbage collector thingy
> >> periodically.
> >> > Lru list needs pressure to age and reorder entries properly.
> >>
> >> Swap the negative dentry to the head of hash list when it get
> >> accessed?
> >> Extra ones can be easily trimmed when swapping, using GC is to
> >> reduce
> >> perf impact?
> >>
> >>
> >> Reclaimer/shrinker scans denties in LRU lists, it's an another list.
> >
> > Ah, you mean GC to reclaim from LRU list. I am not sure it could catch
> > up the speed of negative dentry generating.
> >
> > Thanks,
> >
> > Junxiao.
> >
> >> My patch used order in hash lists is a very unusual way. Don't be
> >> confused.
> >>
> >> There are four lists
> >> parent - siblings
> >> hashtable - hashchain
> >> LRU
> >> inode - alias
> >>
> >>
> >> Thanks,
> >>
> >> Junxioao.
> >>
> >> >
> >> > Gc could be off by default or thresholds set very high (50% of
> >> ram for
> >> > example).
> >> > Final setup could be left up to owners of large systems, which
> >> needs
> >> > fine tuning.
> >>
>
[-- Attachment #2: Type: text/html, Size: 6539 bytes --]
prev parent reply other threads:[~2020-12-17 15:47 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-08 12:23 Konstantin Khlebnikov
2020-05-08 12:23 ` [PATCH RFC 1/8] dcache: show count of hash buckets in sysctl fs.dentry-state Konstantin Khlebnikov
2020-05-08 14:49 ` Waiman Long
2020-05-08 16:16 ` Konstantin Khlebnikov
2020-05-08 19:05 ` Waiman Long
2020-05-08 19:38 ` Konstantin Khlebnikov
2020-05-08 20:00 ` Waiman Long
2020-05-08 20:03 ` Matthew Wilcox
2020-05-08 12:23 ` [PATCH RFC 2/8] selftests: add stress testing tool for dcache Konstantin Khlebnikov
2020-05-13 1:52 ` Dave Chinner
2020-05-08 12:23 ` [PATCH RFC 3/8] dcache: sweep cached negative dentries to the end of list of siblings Konstantin Khlebnikov
2020-05-08 19:38 ` Waiman Long
2020-05-08 12:23 ` [PATCH RFC 4/8] fsnotify: stop walking child dentries if remaining tail is negative Konstantin Khlebnikov
2020-05-08 12:23 ` [PATCH RFC 5/8] dcache: add action D_WALK_SKIP_SIBLINGS to d_walk() Konstantin Khlebnikov
2020-05-08 12:23 ` [PATCH RFC 6/8] dcache: stop walking siblings if remaining dentries all negative Konstantin Khlebnikov
2020-05-08 12:23 ` [PATCH RFC 7/8] dcache: push releasing dentry lock into sweep_negative Konstantin Khlebnikov
2020-05-08 12:23 ` [PATCH RFC 8/8] dcache: prevent flooding with negative dentries Konstantin Khlebnikov
2020-05-08 14:56 ` Matthew Wilcox
2020-05-08 16:29 ` Konstantin Khlebnikov
2020-05-08 21:07 ` Waiman Long
2020-12-09 23:01 ` [PATCH RFC 0/8] dcache: increase poison resistance Junxiao Bi
2020-12-12 7:32 ` Konstantin Khlebnikov
2020-12-13 18:49 ` Junxiao Bi
2020-12-14 7:43 ` Konstantin Khlebnikov
2020-12-14 23:10 ` Junxiao Bi
2020-12-16 18:46 ` Junxiao Bi
2020-12-17 15:47 ` Konstantin Khlebnikov [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CALYGNiPi+dqYgvTRwtcQXGAsdexCifJe4X7NN6tx4etrTcnyjA@mail.gmail.com \
--to=koct9i@gmail.com \
--cc=gautham.ananthakrishna@oracle.com \
--cc=junxiao.bi@oracle.com \
--cc=khlebnikov@yandex-team.ru \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=longman@redhat.com \
--cc=matthew.wilcox@oracle.com \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox