linux-kernel - Re: [PATCH] mm: fix page_mkclean

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Date:	Wed, 27 Dec 2006 22:20:20 -0700
From:	"Gordon Farquharson" <gordonfarquharson@...il.com>
To:	"Linus Torvalds" <torvalds@...l.org>
Cc:	"David Miller" <davem@...emloft.net>, ranma@...edrich.de,
	tbm@...ius.com, "Peter Zijlstra" <a.p.zijlstra@...llo.nl>,
	andrei.popa@...eo.ro, "Andrew Morton" <akpm@...l.org>,
	hugh@...itas.com, nickpiggin@...oo.com.au, arjan@...radead.org,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: fix page_mkclean_one

[Oops - forgot to hit "Reply to All" first time round.]

Hi Linus

On 12/27/06, Linus Torvalds <torvalds@...l.org> wrote:

> For all I know, my test-program is buggy wrt the ordering printouts,
> though. Did you perhaps change the logic in any way?

I don't think so. I did reduce the target size

#define TARGETSIZE (100 << 12)

to make the program finish a little quicker, and for some reason I get

linus-test.c: In function 'remap':
linus-test.c:61: error: 'POSIX_FADV_DONTNEED' undeclared (first use in
this function)

when I compile the program, so I replaced POSIX_FADV_DONTNEED with 4
as defined in /usr/include/bits/fcntl.h.

Other than these two changes, the program is identical to the version
you posted.

I have run the program a few times, and the output is pretty
consistent. However, when I increase the target size, the difference
between the expected and actual values is larger.

Written as (749)935(738)
Chunk 1113 corrupted (1-1455)  (2965-323)
Expected 89, got 93
Written as (935)738(538)
Chunk 1114 corrupted (1-1455)  (329-1783)
Expected 90, got 94
Written as (738)538(678)
Chunk 1115 corrupted (1-1455)  (1789-3243)
Expected 91, got 95
Written as (538)678(989)
Chunk 1120 corrupted (1-1455)  (897-2351)
Expected 96, got 100
Written as (537)265(1005)
Chunk 1121 corrupted (1-1455)  (2357-3811)
Expected 97, got 101
Written as (265)1005(-1)

--- linus-test.c.orig   2006-12-28 06:17:24.000000000 +0100
+++ linus-test.c        2006-12-28 06:18:24.000000000 +0100
@@ -6,7 +6,7 @@
 #include <stdio.h>
 #include <time.h>

-#define TARGETSIZE (100 << 20)
+#define TARGETSIZE (100 << 14)
 #define CHUNKSIZE (1460)
 #define NRCHUNKS (TARGETSIZE / CHUNKSIZE)
 #define SIZE (NRCHUNKS * CHUNKSIZE)
@@ -61,7 +61,7 @@
 {
        if (mapping) {
                munmap(mapping, SIZE);
-                posix_fadvise(fd, 0, SIZE, POSIX_FADV_DONTNEED);
+                posix_fadvise(fd, 0, SIZE, 4);
        }
        return mmap(NULL, SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);

Gordon

-- 
Gordon Farquharson
-
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