linux-kernel - Re: 32-bit bio regression with 4.3 [was: Re: cgroup/loop Bad page state oops in Linux v4.2-rc3-136-g45b4b782e848]

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Message-ID: <CAF1ivSYscP8D66pBhVS_yYaNUmjhwmiw4y-VO_Dbo-GA4E=cqA@mail.gmail.com>
Date:	Fri, 11 Sep 2015 21:43:48 -0700
From:	Ming Lin <mlin@...nel.org>
To:	Mike Snitzer <snitzer@...hat.com>
Cc:	Josh Boyer <jwboyer@...oraproject.org>,
	Joe Thornber <ejt@...hat.com>,
	Ming Lei <ming.lei@...onical.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Tejun Heo <tj@...nel.org>, Jens Axboe <axboe@...com>,
	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
	awilliam@...hat.com
Subject: Re: 32-bit bio regression with 4.3 [was: Re: cgroup/loop Bad page
 state oops in Linux v4.2-rc3-136-g45b4b782e848]

On Fri, Sep 11, 2015 at 2:43 PM, Mike Snitzer <snitzer@...hat.com> wrote:
> Ming, Jens, others:
>
> Please see this BZ comment that speaks to a 4.3 regression due to the
> late bio splitting changes:
> https://bugzilla.redhat.com/show_bug.cgi?id=1247382#c41
>
> But inlined here so we can continue on list:
> (In reply to Josh Boyer from comment #40)
>> The function that was fixed in 4.2 doesn't exist any longer in
>> 4.3.0-0.rc0.git6.1.fc24.  That kernel corresponds to Linux
>> v4.2-6105-gdd5cdb48edfd which contains commit
>> 8ae126660fddbeebb9251a174e6fa45b6ad8f932, which removed it completely.  So
>> whatever fix was made in dm_merge_bvec doesn't seem to have made it to
>> whatever replaced it.
>
> The dm core fix to dm_merge_bvec was commit bd4aaf8f9b ("dm: fix
> dm_merge_bvec regression on 32 bit systems").  But I'm not sure there is
> a clear equivalent in the late bio splitting code that replaced block
> core's merge_bvec logic.
>
> merge_bvec was all about limiting bios (by asking "can/should this page
> be added to this bio?") whereas the late bio splitting is more "build
> the bios as large as possible and worry about splitting later".
>
> Regardless, this regression needs to be reported to Ming Lin
> <ming.l@....samsung.com>, Jens Axboe and the others involved in
> maintaining the late bio splitting changes in block core.

I'm looking at it now.
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