Re: [PATCH] ext4: Fix deadlock on page reclaim

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Dave,

On 2019/07/31 8:48, Dave Chinner wrote:
> On Tue, Jul 30, 2019 at 02:06:33AM +0000, Damien Le Moal wrote:
>> If we had a pread_nofs()/pwrite_nofs(), that would work. Or we could define a
>> RWF_NORECLAIM flag for pwritev2()/preadv2(). This last one could actually be the
>> cleanest approach.
> 
> Clean, yes, but I'm not sure we want to expose kernel memory reclaim
> capabilities to userspace... It would be misleading, too, because we
> still want to allow reclaim to occur, just not have reclaim recurse
> into other filesystems....

When I wrote RWF_NORECLAIM, I was really thinking of RWF_NOFSRECLAIM. So
suppressing direct reclaim recursing into another FS rather than completely
disabling reclaim. Sorry for the confusion.

Would this be better ? This is still application controlled, so debatable if
control should be given. Most likely this would need to be limited to CAP_SYS
capable user processes (e.g. root processes).

I still need to check on FUSE if anything at all along these lines exists there.
I will dig.

Best regards.

-- 
Damien Le Moal
Western Digital Research




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