From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl0-f72.google.com (mail-pl0-f72.google.com [209.85.160.72]) by kanga.kvack.org (Postfix) with ESMTP id 429176B026E for ; Mon, 28 May 2018 11:54:18 -0400 (EDT) Received: by mail-pl0-f72.google.com with SMTP id 31-v6so7813627plf.19 for ; Mon, 28 May 2018 08:54:18 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id p15-v6si88684plq.180.2018.05.28.08.54.16 for (version=TLS1 cipher=AES128-SHA bits=128/128); Mon, 28 May 2018 08:54:17 -0700 (PDT) Date: Mon, 28 May 2018 11:21:38 +0200 From: Michal Hocko Subject: Re: [PATCH] doc: document scope NOFS, NOIO APIs Message-ID: <20180528092138.GI1517@dhcp22.suse.cz> References: <20180424183536.GF30619@thunk.org> <20180524114341.1101-1-mhocko@kernel.org> <20180524221715.GY10363@dastard> <20180525081624.GH11881@dhcp22.suse.cz> <20180527124721.GA4522@rapoport-lnx> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180527124721.GA4522@rapoport-lnx> Sender: owner-linux-mm@kvack.org List-ID: To: Mike Rapoport Cc: Dave Chinner , Jonathan Corbet , LKML , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, "Darrick J. Wong" , David Sterba 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