Message-ID: <4378C626.4030107@rtr.ca>
Date: Mon, 14 Nov 2005 12:15:18 -0500
From: Mark Lord <lkml@rtr.ca>
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To: Badari Pulavarty <pbadari@gmail.com>
Cc: Arjan van de Ven <arjan@infradead.org>,
       Linux Kernel <linux-kernel@vger.kernel.org>
Subject: Re: 2.6.xx:  dirty pages never being sync'd to disk?
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Badari Pulavarty wrote:
>
> Interesting. Since you have a very easy to reproduce case -
> can you write a program to do posix_fadvise(POSIX_FADV_DONTNEED)
> on those files in directory "t" and see what happens ?

Sure.  It appears to cause an immediate "sync" of the file data
to disk (lots of drive activity for a few seconds), and the Dirty
count from /proc/meminfo reduces correspondingly.

Oddly enough, the Dirty count didn't go all the way down, though.
Doing a "sync" or a second run of the program afterwards does
get the count down to zero immediately, without any significant I/O.

Strange.

#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>

int main (int argc, char *argv[])
{
         while (--argc > 0) {
                 int fd = open(*++argv, O_RDWR);
                 if (fd == -1) {
                         perror(*argv);
                 } else {
                         int posix_fadvise(int, off_t, off_t, int);
                         const int POSIX_FADV_DONTNEED = 4;
                         int rc = posix_fadvise(fd, 0, 0, POSIX_FADV_DONTNEED);
                         if (rc == -1)
                                 perror(*argv);
                         close(fd);
                 }
         }
         return 0;
}
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