Re: [PATCH] doc: document scope NOFS, NOIO APIs

[Mike Rapoport]

On Fri, May 25, 2018 at 10:16:24AM +0200, Michal Hocko wrote:
> On Fri 25-05-18 08:17:15, Dave Chinner wrote:
> > On Thu, May 24, 2018 at 01:43:41PM +0200, Michal Hocko wrote:
> [...]
> > > +FS/IO code then simply calls the appropriate save function right at the
> > > +layer where a lock taken from the reclaim context (e.g. shrinker) and
> > > +the corresponding restore function when the lock is released. All that
> > > +ideally along with an explanation what is the reclaim context for easier
> > > +maintenance.
> > 
> > This paragraph doesn't make much sense to me. I think you're trying
> > to say that we should call the appropriate save function "before
> > locks are taken that a reclaim context (e.g a shrinker) might
> > require access to."
> > 
> > I think it's also worth making a note about recursive/nested
> > save/restore stacking, because it's not clear from this description
> > that this is allowed and will work as long as inner save/restore
> > calls are fully nested inside outer save/restore contexts.
> 
> Any better?
> 
> -FS/IO code then simply calls the appropriate save function right at the
> -layer where a lock taken from the reclaim context (e.g. shrinker) and
> -the corresponding restore function when the lock is released. All that
> -ideally along with an explanation what is the reclaim context for easier
> -maintenance.
> +FS/IO code then simply calls the appropriate save function before any
> +lock shared with the reclaim context is taken.  The corresponding
> +restore function when the lock is released. All that ideally along with

Maybe: "The corresponding restore function is called when the lock is
released"

> +an explanation what is the reclaim context for easier maintenance.
> +
> +Please note that the proper pairing of save/restore function allows nesting
> +so memalloc_noio_save is safe to be called from an existing NOIO or NOFS scope.
 
so it is safe to call memalloc_noio_save from an existing NOIO or NOFS
scope

>  What about __vmalloc(GFP_NOFS)
>  ==============================
> -- 
> Michal Hocko
> SUSE Labs
> 

-- 
Sincerely yours,
Mike.