lkml.org 
[lkml]   [2018]   [May]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCH] doc: document scope NOFS, NOIO APIs
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

\
 
 \ /
  Last update: 2018-05-28 17:55    [W:0.806 / U:0.012 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site