Messages in this thread | | | From | Michal Hocko <> | Subject | [RFC 0/2] mapping_gfp_mask from the page fault path | Date | Mon, 1 Jun 2015 15:00:01 +0200 |
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Hi, 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.
The second patch is an attempt to handle mapping_gfp_mask from the page fault path properly. GFP_IOFS should be safe from he page fault path in general (we would be quite broken otherwise because there are places where GFP_KERNEL is used - e.g. pte allocation). MM will communicate this to the fs layer via struct vm_fault::gfp_mask. If fs needs to change this allocation context in a fs callback it can overwrite this mask. If the code flow gets back to MM we will obey this gfp_mask (e.g. in page_cache_read). This should be more appropriate than following mapping_gfp_mask blindly. See the patch description for more details.
I am still not sure this is the right way to go so I am sending this as an RFC so any comments are highly appreciated.
Thanks!
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