Messages in this thread Patch in this message | | | Date | Sun, 26 Feb 2006 22:50:25 +0300 | From | Oleg Nesterov <> | Subject | [PATCH] readahead: fix initial window size calculation |
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(I hope it is ok to send this patch without Steven's reply)
From: Steven Pratt <slpratt@austin.ibm.com>
The current current get_init_ra_size is not optimal across different IO sizes and max_readahead values. Here is a quick summary of sizes computed under current design and under the attached patch. All of these assume 1st IO at offset 0, or 1st detected sequential IO.
32k max, 4k request
old new ----------------- 8k 8k 16k 16k 32k 32k
128k max, 4k request old new ----------------- 32k 16k 64k 32k 128k 64k 128k 128k
128k max, 32k request old new ----------------- 32k 64k <----- 64k 128k 128k 128k
512k max, 4k request old new ----------------- 4k 32k <---- 16k 64k 64k 128k 128k 256k 512k 512k
--- 2.6.16-rc3/mm/readahead.c~ 2006-02-27 00:53:17.881019192 +0300 +++ 2.6.16-rc3/mm/readahead.c 2006-02-27 01:10:39.172718792 +0300 @@ -83,10 +83,10 @@ static unsigned long get_init_ra_size(un { unsigned long newsize = roundup_pow_of_two(size); - if (newsize <= max / 64) - newsize = newsize * newsize; + if (newsize <= max / 32) + newsize = newsize * 4; else if (newsize <= max / 4) - newsize = max / 4; + newsize = newsize * 2; else newsize = max; return newsize; - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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