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

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Date:	Wed, 16 Feb 2011 02:40:49 -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)

Looking at this I believe that delayed allocation is enabled in the disk:

$ cat /sys/fs/ext4/sda5/delayed_allocation_blocks
2

Javi

On Wed, Feb 16, 2011 at 2:33 AM, Javi <javier.cabezas@...il.com> wrote:
> 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
>



-- 
Javi
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