Re: [PATCH] bump up nr_to_write in xfs_vm_writepage

[Chris Mason <chris.mason@oracle.com>]

On Fri, Jul 24, 2009 at 12:20:32AM -0500, Felix Blyakher wrote:
>
> On Jul 10, 2009, at 2:12 AM, KOSAKI Motohiro wrote:
>> 3. Current wbc->nr_to_write value is not proper?
>>
>> Current writeback_set_ratelimit() doesn't permit that ratelimit_pages 
>> exceed
>> 4M byte. but it is too low restriction for nowadays.
>> (that's my understand. right?)
>>
>> =======================================================
>> void writeback_set_ratelimit(void)
>> {
>>        ratelimit_pages = vm_total_pages / (num_online_cpus() * 32);
>>        if (ratelimit_pages < 16)
>>                ratelimit_pages = 16;
>>        if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
>>                ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
>> }
>> =======================================================
>>
>> Yes, 4M bytes are pretty magical constant. We have three choice
>>  A. Remove magical 4M constant simple (a bit danger)
>
> That's will be outside the xfs, and seems like there is no much interest
> from mm people.
>
>>  B. Decide high border from IO capability

It is worth pointing out that Jens Axboe is planning on more feedback
controlled knobs as part of pdflush rework.

-chris

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