linux-ext4 - Re: Heavy disk I/O on temporary mmap'ed files (ext4)

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Date:	Wed, 16 Feb 2011 02:33:22 -0600
From:	Javi <javier.cabezas@...il.com>
To:	Yongqiang Yang <xiaoqiangnk@...il.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: Heavy disk I/O on temporary mmap'ed files (ext4)

I am using the current mount options:

UUID=46fc675c-f196-4be2-bf4d-461d473de6b1 / ext4
errors=remount-ro,user_xattr 0 1

And the dmesg messages I get are:

[    2.908858] EXT4-fs (sda5): mounted filesystem with ordered data
mode. Opts: (null)
[   14.167465] EXT4-fs (sda5): re-mounted. Opts: errors=remount-ro,user_xattr
[   15.512701] EXT4-fs (sda5): re-mounted. Opts:
errors=remount-ro,user_xattr,commit=0
[   20.801609] EXT4-fs (sda5): re-mounted. Opts:
errors=remount-ro,user_xattr,commit=0

How can I give you more information?

Thanks,
  Javi

On Wed, Feb 16, 2011 at 2:12 AM, Yongqiang Yang <xiaoqiangnk@...il.com> wrote:
> Was ext4 mounted with dealloc?
>
> On Mon, Feb 7, 2011 at 3:41 PM, Javi <javier.cabezas@...il.com> wrote:
>>
>> I am developing a software based DSM. In order to avoid concurrent
>> updates on a memory page that is being updated by the runtime I am
>> using a shadow mapping to perform the updates. This mappings are
>> created by opening a file, unlinking it and mmap-ing on the file
>> descriptor. Everything is working but I am experiencing heavy disk I/O
>> during execution on a machine with a single ext4 file system. Other
>> machines that use ext3 partitions don't exhibit this behavior (there
>> is no disk I/O at all). This machine is using the kernel version
>> 2.6.35-25-generic.
>>
>> The exact steps performed to create the mappings are:
>>
>>    // Create the file
>>    snprintf(tmp, FILENAME_MAX, "/tmp/testXXXXXX");
>>    int fd = mkstemp(tmp);
>>    if(fd < 0) return NULL;
>>    unlink(tmp);
>>
>>    if(ftruncate(fd, count) < 0) {
>>        close(fd);
>>        return NULL;
>>    }
>>    ...
>>
>>    // Create a mapping
>>    addr = mmap(NULL, count, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
>>
>>
>> Does ext4 write to mmap'ed files although they don't have a name in
>> the file system? Am I doing anything wrong?
>>
>> Thanks,
>>  Javi
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
>> the body of a message to majordomo@...r.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>
>
>
> --
> Best Wishes
> Yongqiang Yang
>
>



-- 
Javi
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