lkml.org 
[lkml]   [2011]   [Nov]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH 7/7] mm: compaction: Introduce sync-light migration for use by compaction
From
On Tue, Nov 22, 2011 at 2:56 PM, Shaohua Li <shaohua.li@intel.com> wrote:
> On Tue, 2011-11-22 at 02:36 +0800, Mel Gorman wrote:
>> This patch adds a lightweight sync migrate operation MIGRATE_SYNC_LIGHT
>> mode that avoids writing back pages to backing storage. Async
>> compaction maps to MIGRATE_ASYNC while sync compaction maps to
>> MIGRATE_SYNC_LIGHT. For other migrate_pages users such as memory
>> hotplug, MIGRATE_SYNC is used.
>>
>> This avoids sync compaction stalling for an excessive length of time,
>> particularly when copying files to a USB stick where there might be
>> a large number of dirty pages backed by a filesystem that does not
>> support ->writepages.
> Hi,
> from my understanding, with this, even writes
> to /proc/sys/vm/compact_memory doesn't wait for pageout, is this
> intended?
> on the other hand, MIGRATE_SYNC_LIGHT now waits for pagelock and buffer
> lock, so could wait on page read. page read and page out have the same
> latency, why takes them different?

So for the problem you raised, I think my suggestion to Mel is to adopt the
following logic:

if (!trylock_page(page) && !PageUptodate(page))
we are quite likely to block on read, so we
depend on yet another MIGRATE_SYNC_MODE to decide
if we really want to lock_page() and wait for this IO.

How do you think ?


Thanks,

Nai
>
> Thanks,
> Shaohua
>
>


\
 
 \ /
  Last update: 2011-11-23 03:05    [W:0.151 / U:0.040 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site