From: Wu Fengguang <fengguang.wu@intel.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Andi Kleen <andi@firstfloor.org>, Jan Kara <jack@suse.cz>,
Wu Fengguang <fengguang.wu@intel.com>
Cc: Linux Memory Management List <linux-mm@kvack.org>,
<linux-fsdevel@vger.kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>
Subject: [PATCH 8/9] readahead: snap readahead request to EOF
Date: Sat, 11 Feb 2012 12:31:48 +0800 [thread overview]
Message-ID: <20120211043326.531569582@intel.com> (raw)
In-Reply-To: 20120211043140.108656864@intel.com
[-- Attachment #1: readahead-eof --]
[-- Type: text/plain, Size: 1623 bytes --]
If the file size is 20kb and readahead request is [0, 16kb),
it's better to expand the readahead request to [0, 20kb), which will
likely save one followup I/O for the ending [16kb, 20kb).
If the readahead request already covers EOF, trimm it down to EOF.
Also don't set the PG_readahead mark to avoid an unnecessary future
invocation of the readahead code.
This special handling looks worthwhile because small to medium sized
files are pretty common.
Acked-by: Jan Kara <jack@suse.cz>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
mm/readahead.c | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)
--- linux-next.orig/mm/readahead.c 2012-01-25 15:57:58.000000000 +0800
+++ linux-next/mm/readahead.c 2012-01-25 15:57:59.000000000 +0800
@@ -466,6 +466,25 @@ unsigned long max_sane_readahead(unsigne
+ node_page_state(numa_node_id(), NR_FREE_PAGES)) / 2);
}
+static void snap_to_eof(struct file_ra_state *ra, struct address_space *mapping)
+{
+ pgoff_t eof = ((i_size_read(mapping->host)-1) >> PAGE_CACHE_SHIFT) + 1;
+ pgoff_t start = ra->start;
+ unsigned int size = ra->size;
+
+ /*
+ * skip backwards and random reads
+ */
+ if (ra->pattern > RA_PATTERN_MMAP_AROUND)
+ return;
+
+ size += min(size / 2, ra->ra_pages / 4);
+ if (start + size > eof) {
+ ra->size = eof - start;
+ ra->async_size = 0;
+ }
+}
+
/*
* Submit IO for the read-ahead request in file_ra_state.
*/
@@ -477,6 +496,8 @@ unsigned long ra_submit(struct file_ra_s
{
int actual;
+ snap_to_eof(ra, mapping);
+
actual = __do_page_cache_readahead(mapping, filp,
ra->start, ra->size, ra->async_size);
next prev parent reply other threads:[~2012-02-11 9:51 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-11 4:31 [PATCH 0/9] readahead stats/tracing, backwards prefetching and more (v5) Wu Fengguang
2012-02-11 4:31 ` [PATCH 1/9] readahead: make context readahead more conservative Wu Fengguang
2012-02-11 4:31 ` [PATCH 2/9] readahead: record readahead patterns Wu Fengguang
2012-02-11 4:31 ` [PATCH 3/9] readahead: tag mmap page fault call sites Wu Fengguang
2012-02-11 4:31 ` [PATCH 4/9] readahead: tag metadata " Wu Fengguang
2012-02-11 4:31 ` [PATCH 5/9] readahead: add vfs/readahead tracing event Wu Fengguang
2012-02-11 4:31 ` [PATCH 6/9] readahead: add /debug/readahead/stats Wu Fengguang
2012-02-11 4:31 ` [PATCH 7/9] readahead: dont do start-of-file readahead after lseek() Wu Fengguang
2012-02-11 4:31 ` Wu Fengguang [this message]
2012-02-11 4:31 ` [PATCH 9/9] readahead: basic support for backwards prefetching Wu Fengguang
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