Messages in this thread | | | From | Nikita Danilov <> | Date | Tue, 4 Jul 2006 17:12:26 +0400 | Subject | Re: [PATCH] mm: moving dirty pages balancing to pdfludh entirely |
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Ananiev, Leonid I writes: > 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.
When queue is congested---it is, because meta-data (indirect blocks in ext[23] case) have to be read in synchronously before page can be paged out (see comment in mm/vmscan.c:pageout()).
But much more importantly: when direct reclaim skips writing dirty pages from tail of the inactive list, it instead moves these pages to the head of this list, and reclaims clean pages instead. These clean pages are "hotter" than skipped dirty pages, and as has been checked many times already, this is bad, because doing reclaim in LRU order is important.
> > Leonid
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