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SubjectRe: [PATCH] ext4: Fix deadlock on page reclaim
On Sat, Jul 27, 2019 at 08:44:23AM +1000, Dave Chinner wrote:
> >
> > This looks like something that could hit every file systems, so
> > shouldn't we fix this in common code? We could also look into
> > just using memalloc_nofs_save for the page cache allocation path
> > instead of the per-mapping gfp_mask.
>
> I think it has to be the entire IO path - any allocation from the
> underlying filesystem could recurse into the top level filesystem
> and then deadlock if the memory reclaim submits IO or blocks on
> IO completion from the upper filesystem. That's a bloody big hammer
> for something that is only necessary when there are stacked
> filesystems like this....

Yeah.... that's why using memalloc_nofs_save() probably makes the most
sense, and dm_zoned should use that before it calls into ext4.

- Ted

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