From: Matthew Wilcox <willy@infradead.org>
To: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-mm@kvack.org, Alexander Viro <viro@zeniv.linux.org.uk>,
Waiman Long <longman@redhat.com>
Subject: Re: [PATCH RFC 8/8] dcache: prevent flooding with negative dentries
Date: Fri, 8 May 2020 07:56:59 -0700 [thread overview]
Message-ID: <20200508145659.GQ16070@bombadil.infradead.org> (raw)
In-Reply-To: <158894061332.200862.9812452563558764287.stgit@buzz>
On Fri, May 08, 2020 at 03:23:33PM +0300, Konstantin Khlebnikov wrote:
> This patch implements heuristic which detects such scenarios and prevents
> unbounded growth of completely unneeded negative dentries. It keeps up to
> three latest negative dentry in each bucket unless they were referenced.
>
> At first dput of negative dentry when it swept to the tail of siblings
> we'll also clear it's reference flag and look at next dentries in chain.
> Then kill third in series of negative, unused and unreferenced denries.
>
> This way each hash bucket will preserve three negative dentry to let them
> get reference and survive. Adding positive or used dentry into hash chain
> also protects few recent negative dentries. In result total size of dcache
> asymptotically limited by count of buckets and positive or used dentries.
>
> This heuristic isn't bulletproof and solves only most practical case.
> It's easy to deceive: just touch same random name twice.
I'm not sure if that's "easy to deceive" ... My concern with limiting
negative dentries is something like a kernel compilation where there
are many (11 for mm/mmap.c, 9 in general) and there will be a lot of
places where <linux/fs.h> does not exist
-isystem /usr/lib/gcc/x86_64-linux-gnu/9/include
-I../arch/x86/include
-I./arch/x86/include/generated
-I../include
-I./include
-I../arch/x86/include/uapi
-I./arch/x86/include/generated/uapi
-I../include/uapi
-I./include/generated/uapi
-I ../mm
-I ./mm
So it'd be good to know that kernel compilation times are unaffected by
this patch.
next prev parent reply other threads:[~2020-05-08 14:57 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-08 12:23 [PATCH RFC 0/8] dcache: increase poison resistance 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 [this message]
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
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=20200508145659.GQ16070@bombadil.infradead.org \
--to=willy@infradead.org \
--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=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;
as well as URLs for NNTP newsgroup(s).