Re: [RFC PATCH] memalloc_noio: update the comment to make it cleaner

[Xiubo Li]

On 2019/9/18 15:25, Michal Hocko wrote:
> On Wed 18-09-19 04:58:20, xiubli@xxxxxxxxxx wrote:
> > From: Xiubo Li <xiubli@xxxxxxxxxx>
> >
> > The GFP_NOIO means all further allocations will implicitly drop
> > both __GFP_IO and __GFP_FS flags and so they are safe for both the
> > IO critical section and the the critical section from the allocation
> > recursion point of view. Not only the __GFP_IO, which a bit confusing
> > when reading the code or using the save/restore pair.
> Historically GFP_NOIO has always implied GFP_NOFS as well. I can imagine
> that this might come as an surprise for somebody not familiar with the
> code though.

Yeah, it true.

>   I am wondering whether your update of the documentation
> would be better off at __GFP_FS, __GFP_IO resp. GFP_NOFS, GFP_NOIO level.
> This interface is simply a way to set a scoped NO{IO,FS} context.

The "Documentation/core-api/gfp_mask-from-fs-io.rst" is already very 
detail about them all.

This fixing just means to make sure that it won't surprise someone who 
is having a quickly through some code and not familiar much about the 
detail. It may make not much sense ?

Thanks,
BRs
Xiubo


> > Signed-off-by: Xiubo Li <xiubli@xxxxxxxxxx>
> > ---
> >   include/linux/sched/mm.h | 9 +++++----
> >   1 file changed, 5 insertions(+), 4 deletions(-)
> >
> > diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> > index 4a7944078cc3..9bdc97e52de1 100644
> > --- a/include/linux/sched/mm.h
> > +++ b/include/linux/sched/mm.h
> > @@ -211,10 +211,11 @@ static inline void fs_reclaim_release(gfp_t gfp_mask) { }
> >    * memalloc_noio_save - Marks implicit GFP_NOIO allocation scope.
> >    *
> >    * This functions marks the beginning of the GFP_NOIO allocation scope.
> > - * All further allocations will implicitly drop __GFP_IO flag and so
> > - * they are safe for the IO critical section from the allocation recursion
> > - * point of view. Use memalloc_noio_restore to end the scope with flags
> > - * returned by this function.
> > + * All further allocations will implicitly drop __GFP_IO and __GFP_FS
> > + * flags and so they are safe for both the IO critical section and the
> > + * the critical section from the allocation recursion point of view. Use
> > + * memalloc_noio_restore to end the scope with flags returned by this
> > + * function.
> >    *
> >    * This function is safe to be used from any context.
> >    */
> > --
> > 2.21.0