The patch titled
readahead: remove sync/async readahead call dependency
has been added to the -mm tree. Its filename is
readahead-remove-sync-async-readahead-call-dependency.patch
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Subject: readahead: remove sync/async readahead call dependency
From: Wu Fengguang <fengguang.wu@xxxxxxxxx>
The readahead call scheme is error-prone in that it expects the call sites
to check for async readahead after doing a sync one. I.e.
if (!page)
page_cache_sync_readahead();
page = find_get_page();
if (page && PageReadahead(page))
page_cache_async_readahead();
This is because PG_readahead could be set by a sync readahead for the
_current_ newly faulted in page, and the readahead code simply expects one
more callback on the same page to start the async readahead. If the
caller fails to do so, it will miss the PG_readahead bits and never able
to start an async readahead.
Eliminate this insane constraint by piggy-backing the async part into the
current readahead window.
Now if an async readahead should be started immediately after a sync one,
the readahead logic itself will do it. So the following code becomes
valid: (the 'else' in particular)
if (!page)
page_cache_sync_readahead();
else if (PageReadahead(page))
page_cache_async_readahead();
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/readahead.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff -puN mm/readahead.c~readahead-remove-sync-async-readahead-call-dependency mm/readahead.c
--- a/mm/readahead.c~readahead-remove-sync-async-readahead-call-dependency
+++ a/mm/readahead.c
@@ -421,6 +421,16 @@ ondemand_readahead(struct address_space
ra->async_size = ra->size > req_size ? ra->size - req_size : ra->size;
readit:
+ /*
+ * Will this read hit the readahead marker made by itself?
+ * If so, trigger the readahead marker hit now, and merge
+ * the resulted next readahead window into the current one.
+ */
+ if (offset == ra->start && ra->size == ra->async_size) {
+ ra->async_size = get_next_ra_size(ra, max);
+ ra->size += ra->async_size;
+ }
+
return ra_submit(ra, mapping, filp);
}
_
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
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