Messages in this thread Patch in this message | | | Subject | [PATCH] fix readahead breakage for sequential after random reads | From | Miklos Szeredi <> | Date | Mon, 19 Jul 2004 00:30:11 +0200 |
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Hi Andrew,
Current readahead logic is broken when a random read pattern is followed by a long sequential read. The cause is that on a window miss ra->next_size is set to ra->average, but ra->average is only updated at the end of a sequence, so window size will remain 1 until the end of the sequential read.
This patch fixes this by taking the current sequence length into account (code taken from towards end of page_cache_readahead()), and also setting ra->average to a decent value in handle_ra_miss() when sequential access is detected.
Please apply!
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
============================================================================== --- linux-2.6.8-rc2/mm/readahead.c.orig 2004-06-16 07:18:57.000000000 +0200 +++ linux-2.6.8-rc2/mm/readahead.c 2004-07-18 23:52:31.000000000 +0200 @@ -470,7 +470,11 @@ do_io: * pages shall be accessed in the next * current window. */ - ra->next_size = min(ra->average , (unsigned long)max); + average = ra->average; + if (ra->serial_cnt > average) + average = (ra->serial_cnt + ra->average + 1) / 2; + + ra->next_size = min(average , (unsigned long)max); } ra->start = offset; ra->size = ra->next_size; @@ -552,6 +556,7 @@ void handle_ra_miss(struct address_space ra->size = max; ra->ahead_start = 0; ra->ahead_size = 0; + ra->average = max / 2; } } ra->prev_page = offset;
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