Messages in this thread | | | Date | Fri, 04 Jun 2010 15:06:49 +0530 | From | Nitin Gupta <> | Subject | Re: [PATCH V2 0/7] Cleancache (was Transcendent Memory): overview |
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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
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