From: Waiman Long <longman@redhat.com> To: Andrew Morton <akpm@linux-foundation.org>, Matthew Wilcox <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org>, Dave Chinner <david@fromorbit.com>, James Bottomley <James.Bottomley@HansenPartnership.com>, Linus Torvalds <torvalds@linux-foundation.org>, Al Viro <viro@zeniv.linux.org.uk>, Jonathan Corbet <corbet@lwn.net>, "Luis R. Rodriguez" <mcgrof@kernel.org>, Kees Cook <keescook@chromium.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, linux-fsdevel <linux-fsdevel@vger.kernel.org>, linux-mm <linux-mm@kvack.org>, "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>, Jan Kara <jack@suse.cz>, Paul McKenney <paulmck@linux.vnet.ibm.com>, Ingo Molnar <mingo@kernel.org>, Miklos Szeredi <mszeredi@redhat.com>, Larry Woodman <lwoodman@redhat.com>, "Wangkai (Kevin,C)" <wangkai86@huawei.com> Subject: Re: [PATCH v6 0/7] fs/dcache: Track & limit # of negative dentries Date: Wed, 18 Jul 2018 14:39:48 -0400 [thread overview] Message-ID: <d37af7a4-b9a9-0928-eed0-10ab818d08c0@redhat.com> (raw) In-Reply-To: <20180716164032.94e13f765c5f33c6022eca38@linux-foundation.org> On 07/16/2018 07:40 PM, Andrew Morton wrote: > On Mon, 16 Jul 2018 05:41:15 -0700 Matthew Wilcox <willy@infradead.org> wrote: > >> On Mon, Jul 16, 2018 at 11:09:01AM +0200, Michal Hocko wrote: >>> On Fri 13-07-18 10:36:14, Dave Chinner wrote: >>> [...] >>>> By limiting the number of negative dentries in this case, internal >>>> slab fragmentation is reduced such that reclaim cost never gets out >>>> of control. While it appears to "fix" the symptoms, it doesn't >>>> address the underlying problem. It is a partial solution at best but >>>> at worst it's another opaque knob that nobody knows how or when to >>>> tune. >>> Would it help to put all the negative dentries into its own slab cache? >> Maybe the dcache should be more sensitive to its own needs. In __d_alloc, >> it could check whether there are a high proportion of negative dentries >> and start recycling some existing negative dentries. > Well, yes. > > The proposed patchset adds all this background reclaiming. Problem is > a) that background reclaiming sometimes can't keep up so a synchronous > direct-reclaim was added on top and b) reclaiming dentries in the > background will cause non-dentry-allocating tasks to suffer because of > activity from the dentry-allocating tasks, which is inappropriate. I have taken out the background reclaiming in the latest v7 patch for the concern people have on duplicating the reclaim effort. We can always add it back on later on if we want to. > I expect a better design is something like > > __d_alloc() > { > ... > while (too many dentries) > call the dcache shrinker > ... > } > > and that's it. This way we have a hard upper limit and only the tasks > which are creating dentries suffer the cost. Yes, that is certainly one way of doing it. Cheers, Longman
WARNING: multiple messages have this Message-ID (diff)
From: Waiman Long <longman@redhat.com> To: Andrew Morton <akpm@linux-foundation.org>, Matthew Wilcox <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org>, Dave Chinner <david@fromorbit.com>, James Bottomley <James.Bottomley@HansenPartnership.com>, Linus Torvalds <torvalds@linux-foundation.org>, Al Viro <viro@zeniv.linux.org.uk>, Jonathan Corbet <corbet@lwn.net>, "Luis R. Rodriguez" <mcgrof@kernel.org>, Kees Cook <keescook@chromium.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, linux-fsdevel <linux-fsdevel@vger.kernel.org>, linux-mm <linux-mm@kvack.org>, "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>, Jan Kara <jack@suse.cz>, Paul McKenney <paulmck@linux.vnet.ibm.com>, Ingo Molnar <mingo@kernel.org>, Miklos Szeredi <mszeredi@redhat.com>, Larry Woodman <lwoodman@redhat.com>, "Wangkai (Kevin,C)" <wangkai86@huawei.com> Subject: Re: [PATCH v6 0/7] fs/dcache: Track & limit # of negative dentries Date: Wed, 18 Jul 2018 14:39:48 -0400 [thread overview] Message-ID: <d37af7a4-b9a9-0928-eed0-10ab818d08c0@redhat.com> (raw) In-Reply-To: <20180716164032.94e13f765c5f33c6022eca38@linux-foundation.org> On 07/16/2018 07:40 PM, Andrew Morton wrote: > On Mon, 16 Jul 2018 05:41:15 -0700 Matthew Wilcox <willy@infradead.org> wrote: > >> On Mon, Jul 16, 2018 at 11:09:01AM +0200, Michal Hocko wrote: >>> On Fri 13-07-18 10:36:14, Dave Chinner wrote: >>> [...] >>>> By limiting the number of negative dentries in this case, internal >>>> slab fragmentation is reduced such that reclaim cost never gets out >>>> of control. While it appears to "fix" the symptoms, it doesn't >>>> address the underlying problem. It is a partial solution at best but >>>> at worst it's another opaque knob that nobody knows how or when to >>>> tune. >>> Would it help to put all the negative dentries into its own slab cache? >> Maybe the dcache should be more sensitive to its own needs. In __d_alloc, >> it could check whether there are a high proportion of negative dentries >> and start recycling some existing negative dentries. > Well, yes. > > The proposed patchset adds all this background reclaiming. Problem is > a) that background reclaiming sometimes can't keep up so a synchronous > direct-reclaim was added on top and b) reclaiming dentries in the > background will cause non-dentry-allocating tasks to suffer because of > activity from the dentry-allocating tasks, which is inappropriate. I have taken out the background reclaiming in the latest v7 patch for the concern people have on duplicating the reclaim effort. We can always add it back on later on if we want to. > I expect a better design is something like > > __d_alloc() > { > ... > while (too many dentries) > call the dcache shrinker > ... > } > > and that's it. This way we have a hard upper limit and only the tasks > which are creating dentries suffer the cost. Yes, that is certainly one way of doing it. Cheers, Longman -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
next prev parent reply other threads:[~2018-07-18 18:39 UTC|newest] Thread overview: 114+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-07-06 19:32 [PATCH v6 0/7] fs/dcache: Track & limit # of negative dentries Waiman Long 2018-07-06 19:32 ` Waiman Long 2018-07-06 19:32 ` [PATCH v6 1/7] fs/dcache: Track & report number " Waiman Long 2018-07-06 19:32 ` Waiman Long 2018-07-06 19:32 ` [PATCH v6 2/7] fs/dcache: Add sysctl parameter neg-dentry-pc as a soft limit on " Waiman Long 2018-07-06 19:32 ` Waiman Long 2018-07-06 19:32 ` [PATCH v6 3/7] fs/dcache: Enable automatic pruning of " Waiman Long 2018-07-06 19:32 ` Waiman Long 2018-07-06 19:32 ` [PATCH v6 4/7] fs/dcache: Spread negative dentry pruning across multiple CPUs Waiman Long 2018-07-06 19:32 ` Waiman Long 2018-07-06 19:32 ` [PATCH v6 5/7] fs/dcache: Add negative dentries to LRU head initially Waiman Long 2018-07-06 19:32 ` Waiman Long 2018-07-06 19:32 ` [PATCH v6 6/7] fs/dcache: Allow optional enforcement of negative dentry limit Waiman Long 2018-07-06 19:32 ` Waiman Long 2018-07-06 19:32 ` [PATCH v6 7/7] fs/dcache: Allow deconfiguration of negative dentry code to reduce kernel size Waiman Long 2018-07-06 19:32 ` Waiman Long 2018-07-06 21:54 ` Eric Biggers 2018-07-06 21:54 ` Eric Biggers 2018-07-06 22:28 ` [PATCH v6 0/7] fs/dcache: Track & limit # of negative dentries Al Viro 2018-07-06 22:28 ` Al Viro 2018-07-07 3:02 ` Waiman Long 2018-07-07 3:02 ` Waiman Long 2018-07-09 8:19 ` Michal Hocko 2018-07-09 8:19 ` Michal Hocko 2018-07-09 16:01 ` Waiman Long 2018-07-09 16:01 ` Waiman Long 2018-07-10 14:27 ` Michal Hocko 2018-07-10 14:27 ` Michal Hocko 2018-07-10 16:09 ` Waiman Long 2018-07-10 16:09 ` Waiman Long 2018-07-11 10:21 ` Michal Hocko 2018-07-11 10:21 ` Michal Hocko 2018-07-11 15:13 ` Waiman Long 2018-07-11 15:13 ` Waiman Long 2018-07-11 17:42 ` James Bottomley 2018-07-11 17:42 ` James Bottomley 2018-07-11 17:42 ` James Bottomley 2018-07-11 19:07 ` Waiman Long 2018-07-11 19:07 ` Waiman Long 2018-07-11 19:21 ` James Bottomley 2018-07-11 19:21 ` James Bottomley 2018-07-11 19:21 ` James Bottomley 2018-07-11 19:21 ` James Bottomley 2018-07-12 15:54 ` Waiman Long 2018-07-12 15:54 ` Waiman Long 2018-07-12 16:04 ` James Bottomley 2018-07-12 16:04 ` James Bottomley 2018-07-12 16:04 ` James Bottomley 2018-07-12 16:04 ` James Bottomley 2018-07-12 16:26 ` Waiman Long 2018-07-12 16:26 ` Waiman Long 2018-07-12 17:33 ` James Bottomley 2018-07-12 17:33 ` James Bottomley 2018-07-12 17:33 ` James Bottomley 2018-07-12 17:33 ` James Bottomley 2018-07-13 15:32 ` Waiman Long 2018-07-13 15:32 ` Waiman Long 2018-07-12 16:49 ` Matthew Wilcox 2018-07-12 16:49 ` Matthew Wilcox 2018-07-12 17:21 ` James Bottomley 2018-07-12 17:21 ` James Bottomley 2018-07-12 17:21 ` James Bottomley 2018-07-12 17:21 ` James Bottomley 2018-07-12 18:06 ` Linus Torvalds 2018-07-12 19:57 ` James Bottomley 2018-07-12 19:57 ` James Bottomley 2018-07-12 19:57 ` James Bottomley 2018-07-12 19:57 ` James Bottomley 2018-07-13 0:36 ` Dave Chinner 2018-07-13 0:36 ` Dave Chinner 2018-07-13 15:46 ` James Bottomley 2018-07-13 15:46 ` James Bottomley 2018-07-13 15:46 ` James Bottomley 2018-07-13 15:46 ` James Bottomley 2018-07-13 23:17 ` Dave Chinner 2018-07-13 23:17 ` Dave Chinner 2018-07-13 23:17 ` Dave Chinner 2018-07-13 23:17 ` Dave Chinner 2018-07-16 9:10 ` Michal Hocko 2018-07-16 9:10 ` Michal Hocko 2018-07-16 14:42 ` James Bottomley 2018-07-16 14:42 ` James Bottomley 2018-07-16 14:42 ` James Bottomley 2018-07-16 14:42 ` James Bottomley 2018-07-16 9:09 ` Michal Hocko 2018-07-16 9:09 ` Michal Hocko 2018-07-16 9:12 ` Michal Hocko 2018-07-16 9:12 ` Michal Hocko 2018-07-16 12:41 ` Matthew Wilcox 2018-07-16 12:41 ` Matthew Wilcox 2018-07-16 23:40 ` Andrew Morton 2018-07-16 23:40 ` Andrew Morton 2018-07-17 1:30 ` Matthew Wilcox 2018-07-17 1:30 ` Matthew Wilcox 2018-07-17 8:33 ` Michal Hocko 2018-07-17 8:33 ` Michal Hocko 2018-07-19 0:33 ` Dave Chinner 2018-07-19 0:33 ` Dave Chinner 2018-07-19 8:45 ` Michal Hocko 2018-07-19 8:45 ` Michal Hocko 2018-07-19 9:13 ` Jan Kara 2018-07-19 9:13 ` Jan Kara 2018-07-18 18:39 ` Waiman Long [this message] 2018-07-18 18:39 ` Waiman Long 2018-07-18 16:17 ` Waiman Long 2018-07-18 16:17 ` Waiman Long 2018-07-19 8:48 ` Michal Hocko 2018-07-19 8:48 ` Michal Hocko 2018-07-12 8:48 ` Michal Hocko 2018-07-12 8:48 ` Michal Hocko 2018-07-12 16:12 ` Waiman Long 2018-07-12 16:12 ` Waiman Long 2018-07-12 23:16 ` Andrew Morton 2018-07-12 23:16 ` Andrew Morton
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