On 7/17/2014 11:45 PM, Gioh Kim wrote: > > Hi, > > For page migration of CMA, buffer-heads of lru should be dropped. > Please refer to https://lkml.org/lkml/2014/7/4/101 for the history. > > I have two solution to drop bhs. > One is invalidating entire lru. > Another is searching the lru and dropping only one bh that Laura proposed > at https://lkml.org/lkml/2012/8/31/313. > > I'm not sure which has better performance. > So I did performance test on my cortex-a7 platform with Lmbench > that has "File & VM system latencies" test. > I am attaching the results. > The first line is of invalidating entire lru and the second is dropping selected bh. > > File & VM system latencies in microseconds - smaller is better > ------------------------------------------------------------------------------- > Host OS 0K File 10K File Mmap Prot Page 100fd > Create Delete Create Delete Latency Fault Fault selct > --------- ------------- ------ ------ ------ ------ ------- ----- ------- ----- > 10.178.33 Linux 3.10.19 25.1 19.6 32.6 19.7 5098.0 0.666 3.45880 6.506 > 10.178.33 Linux 3.10.19 24.9 19.5 32.3 19.4 5059.0 0.563 3.46380 6.521 > > > I tried several times but the result tells that they are the same under 1% gap > except Protection Fault. > But the latency of Protection Fault is very small and I think it has little effect. > > Therefore we can choose anything but I choose invalidating entire lru. > The try_to_free_buffers() which is calling drop_buffers() is called by many filesystem code. > So I think inserting codes in drop_buffers() can affect the system. > And also we cannot distinguish migration type in drop_buffers(). > > In alloc_contig_range() we can distinguish migration type and invalidate lru if it needs. > I think alloc_contig_range() is proper to deal with bh like following patch. > > Laura, can I have you name on Acked-by line? > Please let me represent my thanks. > > Thanks for any feedback. > > ------------------------------- 8< ---------------------------------- > > From 33c894b1bab9bc26486716f0c62c452d3a04d35d Mon Sep 17 00:00:00 2001 > From: Gioh Kim <gioh.kim@xxxxxxx> > Date: Fri, 18 Jul 2014 13:40:01 +0900 > Subject: [PATCH] CMA/HOTPLUG: clear buffer-head lru before page migration > > The bh must be free to migrate a page at which bh is mapped. > The reference count of bh is increased when it is installed > into lru so that the bh of lru must be freed before migrating the page. > > This frees every bh of lru. We could free only bh of migrating page. > But searching lru costs more than invalidating entire lru. > > Signed-off-by: Gioh Kim <gioh.kim@xxxxxxx> > Acked-by: Laura Abbott <lauraa@xxxxxxxxxxxxxx>\ I'd prefer if you would remove my Acked-by line until I've actually given it :) > --- > mm/page_alloc.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index b99643d4..3b474e0 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -6369,6 +6369,9 @@ int alloc_contig_range(unsigned long start, unsigned long end, > if (ret) > return ret; > > + if (migratetype == MIGRATE_CMA || migratetype == MIGRATE_MOVABLE) > + invalidate_bh_lrus(); > + > ret = __alloc_contig_migrate_range(&cc, start, end); > if (ret) > goto done; I agree with the others that the if (...) check doesn't actually help anything here and should probably be removed. Thanks, Laura -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>