Messages in this thread Patches in this message | | | Date | Thu, 22 Jul 2010 16:52:10 +0800 | From | Wu Fengguang <> | Subject | Re: [PATCH 7/8] writeback: sync old inodes first in background writeback |
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> Some insight on how the other writeback changes that are being floated > around might affect the number of dirty pages reclaim encounters would also > be helpful.
Here is an interesting related problem about the wait_on_page_writeback() call inside shrink_page_list():
http://lkml.org/lkml/2010/4/4/86
The problem is, wait_on_page_writeback() is called too early in the direct reclaim path, which blocks many random/unrelated processes when some slow (USB stick) writeback is on the way.
A simple dd can easily create a big range of dirty pages in the LRU list. Therefore priority can easily go below (DEF_PRIORITY - 2) in a typical desktop, which triggers the lumpy reclaim mode and hence wait_on_page_writeback().
I proposed this patch at the time, which was confirmed to solve the problem:
--- linux-next.orig/mm/vmscan.c 2010-06-24 14:32:03.000000000 +0800 +++ linux-next/mm/vmscan.c 2010-07-22 16:12:34.000000000 +0800 @@ -1650,7 +1650,7 @@ static void set_lumpy_reclaim_mode(int p */ if (sc->order > PAGE_ALLOC_COSTLY_ORDER) sc->lumpy_reclaim_mode = 1; - else if (sc->order && priority < DEF_PRIORITY - 2) + else if (sc->order && priority < DEF_PRIORITY / 2) sc->lumpy_reclaim_mode = 1; else sc->lumpy_reclaim_mode = 0;
However KOSAKI and Minchan raised concerns about raising the bar. I guess this new patch is more problem oriented and acceptable:
--- linux-next.orig/mm/vmscan.c 2010-07-22 16:36:58.000000000 +0800 +++ linux-next/mm/vmscan.c 2010-07-22 16:39:57.000000000 +0800 @@ -1217,7 +1217,8 @@ static unsigned long shrink_inactive_lis count_vm_events(PGDEACTIVATE, nr_active); nr_freed += shrink_page_list(&page_list, sc, - PAGEOUT_IO_SYNC); + priority < DEF_PRIORITY / 3 ? + PAGEOUT_IO_SYNC : PAGEOUT_IO_ASYNC); } nr_reclaimed += nr_freed; Thanks, Fengguang
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