Hello, On 07/18/2014 04:23 PM, Gioh Kim wrote: > > > 2014-07-18 오후 4:50, Marek Szyprowski 쓴 글: >> Hello, >> >> On 2014-07-18 08:45, Gioh Kim wrote: >>> 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> >>> --- >>> 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) >> >> I'm not sure if it really makes sense to check the migratetype here. This check >> doesn't add any new information to the code and make false impression that this >> function can be called for other migratetypes than CMA or MOVABLE. Even if so, >> then invalidating bh_lrus unconditionally will make more sense, IMHO. > > I agree. I cannot understand why alloc_contig_range has an argument of migratetype. > Can the alloc_contig_range is called for other migrate type than CMA/MOVABLE? > > What do you think about removing the argument of migratetype and > checking migratetype (if (migratetype == MIGRATE_CMA || migratetype == MIGRATE_MOVABLE))? > Remove the checking only. Because gigantic page allocation used for hugetlb is using alloc_contig_range(...... MIGRATE_MOVABLE). Thanks. -- Thanks. Zhang Yanfei -- 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