Re: Performance degradation seen after using one list for hot/cold pages.

[Minchan Kim <minchan.kim@gmail.com>]

On Tue, Jun 23, 2009 at 9:06 AM, KAMEZAWA
Hiroyuki<kamezawa.hiroyu@jp.fujitsu.com> wrote:
> On Mon, 22 Jun 2009 17:52:36 +0100
> Mel Gorman <mel@csn.ul.ie> wrote:
>
>> On Mon, Jun 22, 2009 at 11:32:03AM +0000, NARAYANAN GOPALAKRISHNAN wrote:
>> > Hi,
>> >
>> > We are running on VFAT.
>> > We are using iozone performance benchmarking tool (http://www.iozone.org/src/current/iozone3_326.tar) for testing.
>> >
>> > The parameters are
>> > /iozone -A -s10M -e -U /tmp -f /tmp/iozone_file
>> >
>> > Our block driver requires requests to be merged to get the best performance.
>> > This was not happening due to non-contiguous pages in all kernels >= 2.6.25.
>> >
>>
>> Ok, by the looks of things, all the aio_read() requests are due to readahead
>> as opposed to explicit AIO  requests from userspace. In this case, nothing
>> springs to mind that would avoid excessive requests for cold pages.
>>
>> It looks like the simpliest solution is to go with the patch I posted.
>> Does anyone see a better alternative that doesn't branch in rmqueue_bulk()
>> or add back the hot/cold PCP lists?
>>
> No objection.  But 2 questions...
>
>> -        list_add(&page->lru, list);
>> +        if (likely(cold == 0))
>> +            list_add(&page->lru, list);
>> +        else
>> +            list_add_tail(&page->lru, list);
>>          set_page_private(page, migratetype);
>>          list = &page->lru;
>>      }
>
> 1. if (likely(coild == 0))
>        "likely" is necessary ?
>
> 2. Why moving pointer "list" rather than following ?
>
>        if (cold)
>                list_add(&page->lru, list);
>        else
>                list_add_tail(&page->lru, list);


I agree.
We can remove unnecessary list head moving forward.


-- 
Kinds regards,
Minchan Kim

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>