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

[Ananiev, Leonid I]

Nikita Danilov writes:
> What about replacing
>		pdflush_operation(background_writeout, 0);
> with
>  		if (pdflush_operation(background_writeout, 0))
>
>                 writeback_inodes(&wbc);
The is a latency betwean pdflush_operation() call and
writeback_in_progress(bdi) returns true.
As a result writeback_inodes() may be called in next loop before pdflush
is started. Pdflush detects that writeback_in_progress() returns true
for it and will exit.

Leonid
-----Original Message-----
From: Nikita Danilov [mailto:nikita@xxxxxxxxxxxxx] 
Sent: Wednesday, July 05, 2006 6:57 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 writes:
 > > suppose you have more than MAX_PDFLUSH_THREADS
 > Do you consider that the drawback of the patch is in that the value
 > MAX_PDFLUSH_THREADS is not well known high or this limit is not
deleted

I am more concerned, that this patch _limits_ maximal possible writeback
concurrency to MAX_PDFLUSH_THREADS.

 > at all? The limit could be deleted after patching because the line 

That sounds a bit too extreme, given that pdflush is used for a lot of
things other than background write-out.

 > +	if (writeback_in_progress(bdi)) {
 > keeps off creating extra pdflush threads.

What about replacing

 		pdflush_operation(background_writeout, 0);

with

 		if (pdflush_operation(background_writeout, 0))
                /*
                 * Fall back to synchronous writeback if all pdflush
                 * threads are busy.
                 */
                writeback_inodes(&wbc);

? This will combine increased concurrency in your target case (single
writer) with some safety net in the case of multiple writers and
multiple devices.

 > 
 > Leonid

Nikita.
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