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SubjectRe: 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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On Fri, Sep 11, 2015 at 2:43 PM, Mike Snitzer <snitzer@redhat.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@ssi.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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