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Message-ID: <4790570E.80709@google.com> Date: Thu, 17 Jan 2008 23:36:46 -0800 From: Mike Waychison <mikew@...gle.com> To: Fengguang Wu <wfg@...l.ustc.edu.cn> CC: Andrew Morton <akpm@...ux-foundation.org>, Michael Rubin <mrubin@...gle.com>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, linux-kernel@...r.kernel.org, linux-mm@...ck.org Subject: Re: [patch] Converting writeback linked lists to a tree based data structure Fengguang Wu wrote: > On Tue, Jan 15, 2008 at 09:51:49PM -0800, Andrew Morton wrote: >> On Wed, 16 Jan 2008 12:55:07 +0800 Fengguang Wu <wfg@...l.ustc.edu.cn> wrote: >> >>> On Tue, Jan 15, 2008 at 08:42:36PM -0800, Andrew Morton wrote: >>>> On Wed, 16 Jan 2008 12:25:53 +0800 Fengguang Wu <wfg@...l.ustc.edu.cn> wrote: >>>> >>>>> list_heads are OK if we use them for one and only function. >>>> Not really. They're inappropriate when you wish to remember your >>>> position in the list while you dropped the lock (as we must do in >>>> writeback). >>>> >>>> A data structure which permits us to interate across the search key rather >>>> than across the actual storage locations is more appropriate. >>> I totally agree with you. What I mean is to first do the split of >>> functions - into three: ordering, starvation prevention, and blockade >>> waiting. >> Does "ordering" here refer to ordering bt time-of-first-dirty? > > Ordering by dirtied_when or i_ino, either is OK. > >> What is "blockade waiting"? > > Some inodes/pages cannot be synced now for some reason and should be > retried after a while. > >>> Then to do better ordering by adopting radix tree(or rbtree >>> if radix tree is not enough), >> ordering of what? > > Switch from time to location. > Given the way LBAs are located on disk and the fact that rotational latency is a large factor in changing locations of a drive head, any attempts to do a C-SCAN pass are pretty much useless. Further complicating this is any volume management that sits between the fs and the actual storage. A nice feature to have longer term is to have the write_inodes paths for background flushing understand storage congestion _through_ any volume management. This would allow us to back off background flushing on a per spindle basis (when using drives of course) and avoid write congestion in both the io scheduler and in the drive's writecaches, which I believe, but don't have hard evidence, get congested today, knocking the drive into a fifo fashion in firmware. A data structure that allows us to keep a dirtied_when values consistent across back-offs and blocking allows us to further develop the background writeout paths to get to this point (though exposing this congestion information will require more work deeper in the stack). >>> and lastly get rid of the list_heads to >>> avoid locking. Does it sound like a good path? >> I'd have thaought that replacing list_heads with another data structure >> would be a simgle commit. > > That would be easy. s_more_io and s_more_io_wait can all be converted > to radix trees. > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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