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Subject[patch 2/2] readahead nfsd case: fix uninitialized ra_min/ra_max
ra_min/ra_max are not initialized, fix it.

New benchmark numbers on

hda: ST3250820A, ATA DISK drive
hda: max request size: 512KiB
hda: 488397168 sectors (250059 MB) w/8192KiB Cache, CHS=30401/255/63, UDMA(100)

with nfs mount
mount -o tcp,rsize=$((rsize<<10)) localhost:$EXPORT $MNT

rsize stock adaptive
==================================
f
8k 3.07 2.51 -18.2%
32k 2.40 2.17 -9.6%
128k 2.40 2.35 -2.1%
ff
8k 12.44 6.40 -48.6%
32k 14.62 5.46 -62.7%
128k 15.79 5.19 -67.1%
d
8k 2.84 2.48 -12.7%
32k 2.53 1.99 -21.3%
128k 2.18 2.00 -8.3%
dd
8k 8.16 7.99 -2.1%
32k 8.27 6.88 -16.8%
128k 7.75 6.97 -10.1%

The 4 patterns tested are:
f: single file read
ff: double file parallel read
d: single dir read
dd: double dir parallel read

Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
---

--- linux-2.6.19-rc6-mm1.orig/mm/readahead.c
+++ linux-2.6.19-rc6-mm1/mm/readahead.c
@@ -1616,6 +1616,10 @@ page_cache_readahead_adaptive(struct add
unsigned long ra_max;
int ret;

+ /* no read-ahead */
+ if (!ra->ra_pages)
+ return 0;
+
if (page) {
ClearPageReadahead(page);

@@ -1635,9 +1639,6 @@ page_cache_readahead_adaptive(struct add
offset + LAPTOP_POLL_INTERVAL))
return 0;
}
- } else if (ra->flags & RA_FLAG_NFSD) { /* nfsd read */
- ra_size = max_sane_readahead(req_size);
- goto readit;
}

if (page)
@@ -1647,11 +1648,13 @@ page_cache_readahead_adaptive(struct add

get_readahead_bounds(ra, &ra_min, &ra_max);

- /* read-ahead disabled? */
- if (unlikely(!ra_max || !readahead_ratio)) {
- ra_size = max_sane_readahead(req_size);
+ /* read as is */
+ if (!readahead_ratio)
+ goto readit;
+
+ /* nfsd read */
+ if (!page && (ra->flags & RA_FLAG_NFSD))
goto readit;
- }

/*
* Start of file.
@@ -1698,11 +1701,11 @@ page_cache_readahead_adaptive(struct add
return 0;
}

+readit:
/*
* Random read.
*/
ra_size = min(req_size, ra_max);
-readit:
ra_size = __do_page_cache_readahead(mapping, filp, offset, ra_size, 0);

ra_account(ra, RA_EVENT_RANDOM_READ, ra_size);
--
-
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