On 05/28/2018 02:21 AM, Michal Hocko wrote: > 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 Please spell out "with respect to". > +reclaim context or when a transaction context nesting would be possible > +via reclaim. The corresponding restore function when the critical "The corresponding restore ... ends." << That is not a complete sentence. It's missing something. > +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. Please note that the proper pairing of save/restore functions allows nesting so it is safe to call ``memalloc_noio_save`` or ``memalloc_noio_restore`` respectively from an existing NOIO or NOFS scope. > > What about __vmalloc(GFP_NOFS) > ============================== > -- ~Randy
