Subject: + readahead-make-context-readahead-more-conservative.patch added to -mm tree To: fengguang.wu@xxxxxxxxx,miaox@xxxxxxxxxxxxxx,tm@xxxxxx From: akpm@xxxxxxxxxxxxxxxxxxxx Date: Mon, 12 Aug 2013 14:39:09 -0700 The patch titled Subject: readahead: make context readahead more conservative has been added to the -mm tree. Its filename is readahead-make-context-readahead-more-conservative.patch This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/readahead-make-context-readahead-more-conservative.patch and later at http://ozlabs.org/~akpm/mmotm/broken-out/readahead-make-context-readahead-more-conservative.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Fengguang Wu <fengguang.wu@xxxxxxxxx> Subject: readahead: make context readahead more conservative This helps performance on moderately dense random reads on SSD. Transaction-Per-Second numbers provided by Taobao: QPS case ------------------------------------------------------- 7536 disable context readahead totally w/ patch: 7129 slower size rampup and start RA on the 3rd read 6717 slower size rampup w/o patch: 5581 unmodified context readahead Before, readahead will be started whenever reading page N+1 when it happen to read N recently. After patch, we'll only start readahead when *three* random reads happen to access pages N, N+1, N+2. The probability of this happening is extremely low for pure random reads, unless they are very dense, which actually deserves some readahead. Also start with a smaller readahead window. The impact to interleaved sequential reads should be small, because for a long run stream, the the small readahead window rampup phase is negletable. The context readahead actually benefits clustered random reads on HDD whose seek cost is pretty high. However as SSD is increasingly used for random read workloads it's better for the context readahead to concentrate on interleaved sequential reads. Another SSD rand read test from Miao # file size: 2GB # read IO amount: 625MB sysbench --test=fileio \ --max-requests=10000 \ --num-threads=1 \ --file-num=1 \ --file-block-size=64K \ --file-test-mode=rndrd \ --file-fsync-freq=0 \ --file-fsync-end=off run shows the performance of btrfs grows up from 69MB/s to 121MB/s, ext4 from 104MB/s to 121MB/s. Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx> Tested-by: Tao Ma <tm@xxxxxx> Tested-by: Miao Xie <miaox@xxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/readahead.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff -puN mm/readahead.c~readahead-make-context-readahead-more-conservative mm/readahead.c --- a/mm/readahead.c~readahead-make-context-readahead-more-conservative +++ a/mm/readahead.c @@ -371,10 +371,10 @@ static int try_context_readahead(struct size = count_history_pages(mapping, ra, offset, max); /* - * no history pages: + * not enough history pages: * it could be a random read */ - if (!size) + if (size <= req_size) return 0; /* @@ -385,8 +385,8 @@ static int try_context_readahead(struct size *= 2; ra->start = offset; - ra->size = get_init_ra_size(size + req_size, max); - ra->async_size = ra->size; + ra->size = min(size + req_size, max); + ra->async_size = 1; return 1; } _ Patches currently in -mm which might be from fengguang.wu@xxxxxxxxx are linux-next.patch watchdog-update-watchdog_tresh-properly-fix.patch thp-account-anon-transparent-huge-pages-into-nr_anon_pages.patch mm-cleanup-add_to_page_cache_locked.patch thp-move-maybe_pmd_mkwrite-out-of-mk_huge_pmd.patch thp-do_huge_pmd_anonymous_page-cleanup.patch thp-consolidate-code-between-handle_mm_fault-and-do_huge_pmd_anonymous_page.patch readahead-make-context-readahead-more-conservative.patch swap-add-a-simple-detector-for-inappropriate-swapin-readahead.patch swap-add-a-simple-detector-for-inappropriate-swapin-readahead-fix.patch smp-give-warning-when-calling-smp_call_function_many-single-in-serving-irq.patch fat-additions-to-support-fat_fallocate-fix.patch vmcore-introduce-remap_oldmem_pfn_range-fix.patch debugging-keep-track-of-page-owners-fix-2-fix-fix-fix.patch debugging-keep-track-of-page-owner-now-depends-on-stacktrace_support.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html