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Date: Mon, 16 Jul 2018 11:12:22 +0200
From: Michal Hocko <mhocko@kernel.org>
To: Dave Chinner <david@fromorbit.com>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Matthew Wilcox <willy@infradead.org>,
	Waiman Long <longman@redhat.com>, 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>,
	Andrew Morton <akpm@linux-foundation.org>,
	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
Message-ID: <20180716091222.GI17280@dhcp22.suse.cz>
References: <18c5cbfe-403b-bb2b-1d11-19d324ec6234@redhat.com>
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 <1531411494.18255.6.camel@HansenPartnership.com>
 <20180712164932.GA3475@bombadil.infradead.org>
 <1531416080.18255.8.camel@HansenPartnership.com>
 <CA+55aFzfQz7c8pcMfLDaRNReNF2HaKJGoWpgB6caQjNAyjg-hA@mail.gmail.com>
 <1531425435.18255.17.camel@HansenPartnership.com>
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On Mon 16-07-18 11:09:01, 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?

We couldn't http://lkml.kernel.org/r/20180714173516.uumlhs4wgfgrlc32@devuan
Sorry I haven't noticed the other line of discussion
-- 
Michal Hocko
SUSE Labs