On Sun 27-05-18 15:47:22, Mike Rapoport wrote: > 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" This will get rewritten some more based on comments from Dave > > +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 Here is what I have right now on top diff --git a/Documentation/core-api/gfp_mask-from-fs-io.rst b/Documentation/core-api/gfp_mask-from-fs-io.rst index c0ec212d6773..0cff411693ab 100644 --- a/Documentation/core-api/gfp_mask-from-fs-io.rst +++ b/Documentation/core-api/gfp_mask-from-fs-io.rst @@ -34,12 +34,15 @@ scope will inherently drop __GFP_FS respectively __GFP_IO from the given mask so no memory allocation can recurse back in the FS/IO. 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 -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. +critical section wrt. the reclaim is started - e.g. lock shared with the +reclaim context or when a transaction context nesting would be possible +via reclaim. The corresponding restore function when the critical +section ends. All that ideally along with an explanation what is +the reclaim context for easier maintenance. + +Please note that the proper pairing of save/restore function allows +nesting so it is safe to call ``memalloc_noio_save`` respectively +``memalloc_noio_restore`` from an existing NOIO or NOFS scope. What about __vmalloc(GFP_NOFS) ============================== -- Michal Hocko SUSE Labs
