Re: [PATCH] readahead: fix initial window size calculation
- From: Steven Pratt <slpratt@xxxxxxxxxxxxxx>
- Date: Mon, 27 Feb 2006 09:41:59 -0600
Oleg Nesterov wrote:
(I hope it is ok to send this patch without Steven's reply)
Yes, It is fine.
From: Steven Pratt <slpratt@xxxxxxxxxxxxxx>
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;
-
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- References:
- [PATCH] readahead: fix initial window size calculation
- From: Oleg Nesterov
- [PATCH] readahead: fix initial window size calculation
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