From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f71.google.com (mail-wm0-f71.google.com [74.125.82.71]) by kanga.kvack.org (Postfix) with ESMTP id C44086B000D for ; Sat, 14 Jul 2018 13:35:28 -0400 (EDT) Received: by mail-wm0-f71.google.com with SMTP id o1-v6so7992982wmc.6 for ; Sat, 14 Jul 2018 10:35:28 -0700 (PDT) Received: from atrey.karlin.mff.cuni.cz (atrey.karlin.mff.cuni.cz. [195.113.26.193]) by mx.google.com with ESMTPS id h9-v6si6589322wmh.53.2018.07.14.10.35.27 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 14 Jul 2018 10:35:27 -0700 (PDT) Date: Sat, 14 Jul 2018 19:35:16 +0200 From: Pavel Machek Subject: Re: [PATCH v5 0/6] fs/dcache: Track & limit # of negative dentries Message-ID: <20180714173516.uumlhs4wgfgrlc32@devuan> References: <1530510723-24814-1-git-send-email-longman@redhat.com> <20180702141811.ef027fd7d8087b7fb2ba0cce@linux-foundation.org> <1530570880.3179.9.camel@HansenPartnership.com> <20180702161925.1c717283dd2bd4a221bc987c@linux-foundation.org> <20180703091821.oiywpdxd6rhtxl4p@quack2.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180703091821.oiywpdxd6rhtxl4p@quack2.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Jan Kara Cc: Andrew Morton , James Bottomley , Linus Torvalds , Waiman Long , Al Viro , Linux Kernel Mailing List , linux-fsdevel , Paul McKenney , Ingo Molnar , Miklos Szeredi , Matthew Wilcox , Larry Woodman , "Wangkai (Kevin,C)" , linux-mm@kvack.org, Michal Hocko > > Yes, "should be". I could understand that the presence of huge > > nunmbers of -ve dentries could result in undesirable reclaim of > > pagecache, etc. Triggering oom-killings is very bad, and presumably > > has the same cause. > > > > Before we go and add a large amount of code to do the shrinker's job > > for it, we should get a full understanding of what's going wrong. Is > > it because the dentry_lru had a mixture of +ve and -ve dentries? > > Should we have a separate LRU for -ve dentries? Are we appropriately > > aging the various dentries? etc. > > > > It could be that tuning/fixing the current code will fix whatever > > problems inspired this patchset. > > What I think is contributing to the problems and could lead to reclaim > oddities is the internal fragmentation of dentry slab cache. Dentries are > relatively small, you get 21 per page on my system, so if trivial to > reclaim negative dentries get mixed with a small amount of unreclaimable > positive dentries, you can get a lot of pages in dentry slab cache that are > unreclaimable. Could we allocate -ve entries from separate slab? -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html