Re: squashfs performance regression and readahea

[Phillip Lougher <phillip@squashfs.org.uk>]

On 09/05/2022 14:21, Matthew Wilcox wrote:
> On Mon, May 09, 2022 at 08:43:45PM +0800, Xiongwei Song wrote:
>> Hi Hsin-Yi and Matthew,
>>
>> With the patch from the attachment on linux 5.10, ran the command as I
>> mentioned earlier,
>> got the results below:
>> 1:40.65 (1m + 40.65s)
>> 1:10.12
>> 1:11.10
>> 1:11.47
>> 1:11.59
>> 1:11.94
>> 1:11.86
>> 1:12.04
>> 1:12.21
>> 1:12.06
>>
>> The performance has improved obviously, but compared to linux 4.18, the
>> performance is not so good.
>>
>> Moreover, I wanted to test on linux 5.18. But I think I should revert
>> 9eec1d897139 ("squashfs: provide backing_dev_info in order to disable
>> read-ahead"),
>> right?  Otherwise, the patch doesn't work?
> 
> I've never seen patch 9eec1d897139 before.  If you're going to point
> out bugs in my code, at least have the decency to cc me on it.  It
> should never have gone in, and should be reverted so the problem can
> be fixed properly.

You are not in charge of what patches goes into Squashfs, that is my
perogative as maintainer of Squashfs.

That patch (by Huawei) fixes the performance regression in Squashfs
by disabling readahead, and it is good workaround until something
better.

If the patch being worked-on now, once reviewed is acceptable, it can
replace the current workaround, which will be reverted.

Cheers

Dr. Phillip Lougher
--
Squashfs author and maintainer.