Re: [RFC 0/2] mapping_gfp_mask from the page fault path

[Andrew Morton]

On Mon,  1 Jun 2015 15:00:01 +0200 Michal Hocko <mhocko@xxxxxxx> wrote:

> I somehow forgot about these patches. The previous version was
> posted here: http://marc.info/?l=linux-mm&m=142668784122763&w=2. The
> first attempt was broken but even when fixed it seems like ignoring
> mapping_gfp_mask in page_cache_read is too fragile because
> filesystems might use locks in their filemap_fault handlers
> which could trigger recursion problems as pointed out by Dave
> http://marc.info/?l=linux-mm&m=142682332032293&w=2.
> 
> The first patch should be straightforward fix to obey mapping_gfp_mask
> when allocating for mapping. It can be applied even without the second
> one.

I'm not so sure about that.  If only [1/2] is applied then those
filesystems which are setting mapping_gfp_mask to GFP_NOFS will now
actually start using GFP_NOFS from within page_cache_read() etc.  The
weaker allocation mode might cause problems.

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