linux-ext4 - Re: problem(?) in ext4 or mke2fs

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Message-ID: <4D98C8B6.7050806@redhat.com>
Date:	Sun, 03 Apr 2011 12:21:26 -0700
From:	Eric Sandeen <sandeen@...hat.com>
To:	Zeev Tarantov <zeev.tarantov@...il.com>
CC:	linux-ext4@...r.kernel.org
Subject: Re: problem(?) in ext4 or mke2fs

On 4/3/11 12:01 PM, Zeev Tarantov wrote:
> On Sun, Apr 3, 2011 at 21:56, Eric Sandeen <sandeen@...hat.com> wrote:
>> On 4/3/11 11:52 AM, Zeev Tarantov wrote:
>>> If the filesystem created with the default options is slow or has
>>> higher cpu usage, it should be changed.
>>
>> I agree.  For actual striped storage, this makes it faster, but this
>> case is a problem; block-sized stripe width is never going to be good.
>> What device is this, exactly?
> 
> Look in linux-2.6/drivers/staging/zram/zram.txt

OK, so it does:

        /*
         * To ensure that we always get PAGE_SIZE aligned
         * and n*PAGE_SIZED sized I/O requests.
         */
        blk_queue_physical_block_size(zram->disk->queue, PAGE_SIZE);
        blk_queue_logical_block_size(zram->disk->queue,
                                        ZRAM_LOGICAL_BLOCK_SIZE);
        blk_queue_io_min(zram->disk->queue, PAGE_SIZE);
        blk_queue_io_opt(zram->disk->queue, PAGE_SIZE);

These are all documented in Documentation/ABI/testing/sysfs-block.

I don't think that setting all those values in zram is necessary and/or
sufficient to achieve what is desired in the comment.  io_min/io_opt
generally are set only for striped devices.

Still, mke2fsprogs should probably sanity-check for this; I'll make
sure this seems right, and send a patch.

Thanks,
-Eric

>> -Eric (losing my free airport wifi in about 8 minutes, so I may have
>> to continue this later...!)
>>
>>>> -Eric
>>>
>>> -Z.T.
>>

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