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

[Nikita Danilov <nikita@clusterfs.com>]

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.