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Date: Mon, 15 Feb 2010 16:47:51 +0100 From: Jan Kara <jack@...e.cz> To: Andrew Morton <akpm@...ux-foundation.org> Cc: Jan Kara <jack@...e.cz>, LKML <linux-kernel@...r.kernel.org>, npiggin@...e.de, fengguang.wu@...el.com Subject: Re: [PATCH 2/3] mm: Implement writeback livelock avoidance using page tagging On Fri 12-02-10 11:39:55, Andrew Morton wrote: > On Fri, 12 Feb 2010 00:06:23 +0100 > Jan Kara <jack@...e.cz> wrote: > > > The idea is simple: Tag all pages that should be written back > > with a special tag (TOWRITE) in the radix tree. This can be done > > rather quickly and thus livelocks should not happen in practice. > > Then we start doing the hard work of locking pages and sending > > them to disk only for those pages that have TOWRITE tag set. > > Adding a second pass across all the pages sounds expensive? Strictly speaking it's just through the radix tree and only through branches with DIRTY_TAG set. But yes, there is some additional CPU cost. I just thought that given the total cost of submitting a page it is an acceptable increase and the simplification is worth it. Would some numbers make you happier? Any suggestion for measurements? Because I think that even for writes to tmpfs the change will be lost in the noise... Honza -- Jan Kara <jack@...e.cz> SUSE Labs, CR -- 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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