The patch titled
readahead: trigger mmap sequential readahead on PG_readahead
has been added to the -mm tree. Its filename is
readahead-trigger-mmap-sequential-readahead-on-pg_readahead.patch
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------------------------------------------------------
Subject: readahead: trigger mmap sequential readahead on PG_readahead
From: Wu Fengguang <fengguang.wu@xxxxxxxxx>
Previously the mmap sequential readahead is triggered by updating
ra->prev_pos on each page fault and compare it with current page offset.
In the mosbench exim benchmark which does multi-threaded page faults on
shared struct file, the ra->mmap_miss and ra->prev_pos updates are found
to cause excessive cache line bouncing on tmpfs, which actually disabled
readahead totally (shmem_backing_dev_info.ra_pages == 0).
So remove the ra->prev_pos recording, and instead tag PG_readahead to
trigger the possible sequential readahead. It's not only more simple, but
also will work more reliably on concurrent reads on shared struct file.
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
Tested-by: Tim Chen <tim.c.chen@xxxxxxxxx>
Reported-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/filemap.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
diff -puN mm/filemap.c~readahead-trigger-mmap-sequential-readahead-on-pg_readahead mm/filemap.c
--- a/mm/filemap.c~readahead-trigger-mmap-sequential-readahead-on-pg_readahead
+++ a/mm/filemap.c
@@ -1570,8 +1570,7 @@ static void do_sync_mmap_readahead(struc
if (!ra->ra_pages)
return;
- if (VM_SequentialReadHint(vma) ||
- offset - 1 == (ra->prev_pos >> PAGE_CACHE_SHIFT)) {
+ if (VM_SequentialReadHint(vma)) {
page_cache_sync_readahead(mapping, ra, file, offset,
ra->ra_pages);
return;
@@ -1594,7 +1593,7 @@ static void do_sync_mmap_readahead(struc
ra_pages = max_sane_readahead(ra->ra_pages);
ra->start = max_t(long, 0, offset - ra_pages / 2);
ra->size = ra_pages;
- ra->async_size = 0;
+ ra->async_size = ra_pages / 4;
ra_submit(ra, mapping, file);
}
@@ -1700,7 +1699,6 @@ retry_find:
return VM_FAULT_SIGBUS;
}
- ra->prev_pos = (loff_t)offset << PAGE_CACHE_SHIFT;
vmf->page = page;
return ret | VM_FAULT_LOCKED;
_
Patches currently in -mm which might be from fengguang.wu@xxxxxxxxx are
mm-per-node-vmstat-show-proper-vmstats.patch
mm-per-node-vmstat-show-proper-vmstats-fix.patch
writeback-pass-writeback_control-down-to-move_expired_inodes.patch
writeback-introduce-writeback_controlinodes_cleaned.patch
writeback-try-more-writeback-as-long-as-something-was-written.patch
writeback-the-kupdate-expire-timestamp-should-be-a-moving-target.patch
writeback-sync-expired-inodes-first-in-background-writeback.patch
writeback-sync-expired-inodes-first-in-background-writeback-fix.patch
writeback-refill-b_io-iff-empty.patch
readahead-readahead-page-allocations-are-ok-to-fail.patch
readahead-return-early-when-readahead-is-disabled.patch
readahead-reduce-unnecessary-mmap_miss-increases.patch
readahead-trigger-mmap-sequential-readahead-on-pg_readahead.patch
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