RE: [PATCH] mm: moving dirty pages balancing to pdfludh entirely

[Ananiev, Leonid I]

Nikita Danilov writes:

> With your patch, this work is done from
> pdflush, and won't be throttled by may_write_to_queue() check, thus
> increasing a risk of allocation failure.
....
After Nikita Danilov agrees that
> pdflush is throttled through blk_congestion_wait(), but it is not
> throttled by writing dirty from the tail of inactive list

The 'writing dirty from the tail of inactive list' is asynchronous
writing and it is not applicable for throttling.

Leonid 
 

-----Original Message-----
From: Nikita Danilov [mailto:nikita@xxxxxxxxxxxxx] 
Sent: Tuesday, July 04, 2006 3:56 PM
To: Ananiev, Leonid I
Cc: Linux Kernel Mailing List
Subject: Re: [PATCH] mm: moving dirty pages balancing to pdfludh
entirely

Ananiev, Leonid I writes:
 > Nikita Danilov wtites:
 > >> Pdflush thread functions as before patching. Pdflush tends to make
 > pages
 > >> un-dirty without overload memory or IO and it is not need to let
 > pdflush
 > 
 > > This assumption is valid for ext2
 > 
 > The assumption that pdflush should to make pages un-dirty without
 > overload memory or IO is not for ext2 but for it sense. I'm working
with

I am not sure what "sense" is being referred to. Some file systems do
allocate a lot of memory in ->writepages().

ext3 is still in the same ball-park as ext2.

 > ext3. A lot of work it does while writepages(). pdflush is throttled:
 > while vmscan have sorted 32 page for paging-out it calls
 > blk_congestion_wait() nevertheless had it put one of 32 page into
 > congested queue or had not. pdflush is throttled.

pdflush is throttled through blk_congestion_wait(), but it is not
throttled by writing dirty from the tail of inactive list, while
scanning for memory. This destroys LRU ordering.

 > 
 > Leonid
 >  

Nikita.
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