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Date: Fri, 04 Jun 2010 15:06:49 +0530 From: Nitin Gupta <ngupta@...are.org> To: Dan Magenheimer <dan.magenheimer@...cle.com> CC: andreas.dilger@...cle.com, Minchan Kim <minchan.kim@...il.com>, chris.mason@...cle.com, viro@...iv.linux.org.uk, akpm@...ux-foundation.org, adilger@....com, tytso@....edu, mfasheh@...e.com, joel.becker@...cle.com, matthew@....cx, linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org, ocfs2-devel@....oracle.com, linux-mm@...ck.org, jeremy@...p.org, JBeulich@...ell.com, kurt.hackel@...cle.com, npiggin@...e.de, dave.mccracken@...cle.com, riel@...hat.com, avi@...hat.com, konrad.wilk@...cle.com Subject: Re: [PATCH V2 0/7] Cleancache (was Transcendent Memory): overview On 06/03/2010 09:13 PM, Dan Magenheimer wrote: >> On 06/03/2010 10:23 AM, Andreas Dilger wrote: >>> On 2010-06-02, at 20:46, Nitin Gupta wrote: >> >>> I was thinking it would be quite clever to do compression in, say, >>> 64kB or 128kB chunks in a mapping (to get decent compression) and >>> then write these compressed chunks directly from the page cache >>> to disk in btrfs and/or a revived compressed ext4. >> >> Batching of pages to get good compression ratio seems doable. > > Is there evidence that batching a set of random individual 4K > pages will have a significantly better compression ratio than > compressing the pages separately? I certainly understand that > if the pages are from the same file, compression is likely to > be better, but pages evicted from the page cache (which is > the source for all cleancache_puts) are likely to be quite a > bit more random than that, aren't they? > Batching of pages from random files may not be so effective but it would be interesting to collect some data for this. Still, per-inode batching of pages seems doable and this should help us get over this problem. Thanks, Nitin -- 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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