The patch titled
readahead: sequential mmap readahead
has been added to the -mm tree. Its filename is
readahead-sequential-mmap-readahead.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 ***
See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find
out what to do about this
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: readahead: sequential mmap readahead
From: Wu Fengguang <fengguang.wu@xxxxxxxxx>
Auto-detect sequential mmap reads and do readahead for them.
The sequential mmap readahead will be triggered when
- sync readahead: it's a major fault and (prev_offset == offset-1);
- async readahead: minor fault on PG_readahead page with valid readahead state.
The benefits of doing readahead instead of read-around:
- less I/O wait thanks to async readahead
- double real I/O size and no more cache hits
The single stream case is improved a little.
For 100,000 sequential mmap reads:
user system cpu total
(1-1) plain -mm, 128KB readaround: 3.224 2.554 48.40% 11.838
(1-2) plain -mm, 256KB readaround: 3.170 2.392 46.20% 11.976
(2) patched -mm, 128KB readahead: 3.117 2.448 47.33% 11.607
The patched (2) has smallest total time, since it has no cache hit overheads
and less I/O block time(thanks to async readahead). Here the I/O size
makes no much difference, since there's only one single stream.
Note that (1-1)'s real I/O size is 64KB and (1-2)'s real I/O size is 128KB,
since the half of the read-around pages will be readahead cache hits.
This is going to make _real_ differences for _concurrent_ IO streams.
Cc: Nick Piggin <npiggin@xxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
Cc: Ying Han <yinghan@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/filemap.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff -puN mm/filemap.c~readahead-sequential-mmap-readahead mm/filemap.c
--- a/mm/filemap.c~readahead-sequential-mmap-readahead
+++ a/mm/filemap.c
@@ -1471,7 +1471,8 @@ static void do_sync_mmap_readahead(struc
if (VM_RandomReadHint(vma))
return;
- if (VM_SequentialReadHint(vma)) {
+ if (VM_SequentialReadHint(vma) ||
+ offset - 1 == (ra->prev_pos >> PAGE_CACHE_SHIFT)) {
page_cache_sync_readahead(mapping, ra, file, offset, 1);
return;
}
_
Patches currently in -mm which might be from fengguang.wu@xxxxxxxxx are
linux-next.patch
readahead-make-mmap_miss-an-unsigned-int.patch
readahead-move-max_sane_readahead-calls-into-force_page_cache_readahead.patch
readahead-apply-max_sane_readahead-limit-in-ondemand_readahead.patch
readahead-remove-one-unnecessary-radix-tree-lookup.patch
readahead-increase-interleaved-readahead-size.patch
readahead-remove-sync-async-readahead-call-dependency.patch
readahead-clean-up-and-simplify-the-code-for-filemap-page-fault-readahead.patch
readahead-sequential-mmap-readahead.patch
readahead-enforce-full-readahead-size-on-async-mmap-readahead.patch
readahead-record-mmap-read-around-states-in-file_ra_state.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
