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
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------------------------------------------------------
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
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