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SubjectRe: fio mmap sequential read 30% regression
On Thu, Jul 02, 2009 at 04:01:22PM +0800, Zhang, Yanmin wrote:
> Comapring with 2.6.30's result, fio mmap sequtial read has
> about 30% regression on one of my stoakley machine with 1
> JBOD (7 SAS disks) with kernel 2.6.31-rc1.
>
> Every disk has 2 partitions and 4 1-GB files per partition. Start
> 10 processes per disk to do mmap read sequentinally.
>
> Bisect down to below patch.
>
> ef00e08e26dd5d84271ef706262506b82195e752 is first bad commit
> commit ef00e08e26dd5d84271ef706262506b82195e752
> Author: Linus Torvalds <torvalds@linux-foundation.org>
> Date: Tue Jun 16 15:31:25 2009 -0700
>
> readahead: clean up and simplify the code for filemap page fault readahead
>
> This shouldn't really change behavior all that much, but the single rather
> complex function with read-ahead inside a loop etc is broken up into more
> manageable pieces.
>
> The behaviour is also less subtle, with the read-ahead being done up-front
> rather than inside some subtle loop and thus avoiding the now unnecessary
> extra state variables (ie "did_readaround" is gone).
>
> Fengguang: the code split in fact fixed a bug reported by Pavel Levshin:
> the PGMAJFAULT accounting used to be bypassed when MADV_RANDOM is set, in
> which case the original code will directly jump to no_cached_page reading.
>
>
> The bisect is stable.

Let me take care of this bug: it may well be caused by my other readahead patches.

Thanks,
Fengguang

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