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SubjectRe: vmalloc with GFP_NOFS


On Tue, 24 Apr 2018, Michal Hocko wrote:

> On Wed 25-04-18 00:18:40, Richard Weinberger wrote:
> > Am Dienstag, 24. April 2018, 21:28:03 CEST schrieb Michal Hocko:
> > > > Also only for debugging.
> > > > Getting rid of vmalloc with GFP_NOFS in UBIFS is no big problem.
> > > > I can prepare a patch.
> > >
> > > Cool!
> > >
> > > Anyway, if UBIFS has some reclaim recursion critical sections in general
> > > it would be really great to have them documented and that is where the
> > > scope api is really handy. Just add the scope and document what is the
> > > recursion issue. This will help people reading the code as well. Ideally
> > > there shouldn't be any explicit GFP_NOFS in the code.
> >
> > So in a perfect world a filesystem calls memalloc_nofs_save/restore and
> > always uses GFP_KERNEL for kmalloc/vmalloc?
>
> Exactly! And in a dream world those memalloc_nofs_save act as a
> documentation of the reclaim recursion documentation ;)
> --
> Michal Hocko
> SUSE Labs

BTW. should memalloc_nofs_save and memalloc_noio_save be merged into just
one that prevents both I/O and FS recursion?

memalloc_nofs_save allows submitting bios to I/O stack and the bios
created under memalloc_nofs_save could be sent to the loop device and the
loop device calls the filesystem...

Mikulas

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