From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1AD85C1B0D8 for ; Thu, 17 Dec 2020 03:07:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BFE0A23719 for ; Thu, 17 Dec 2020 03:07:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727202AbgLQDHA (ORCPT ); Wed, 16 Dec 2020 22:07:00 -0500 Received: from mail106.syd.optusnet.com.au ([211.29.132.42]:48319 "EHLO mail106.syd.optusnet.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725988AbgLQDG7 (ORCPT ); Wed, 16 Dec 2020 22:06:59 -0500 Received: from dread.disaster.area (pa49-179-6-140.pa.nsw.optusnet.com.au [49.179.6.140]) by mail106.syd.optusnet.com.au (Postfix) with ESMTPS id 53DC35AE4BD; Thu, 17 Dec 2020 14:06:14 +1100 (AEDT) Received: from dave by dread.disaster.area with local (Exim 4.92.3) (envelope-from ) id 1kpjcH-004mBp-SK; Thu, 17 Dec 2020 14:06:09 +1100 Date: Thu, 17 Dec 2020 14:06:09 +1100 From: Dave Chinner To: Yafang Shao Cc: darrick.wong@oracle.com, willy@infradead.org, hch@infradead.org, mhocko@kernel.org, akpm@linux-foundation.org, dhowells@redhat.com, jlayton@redhat.com, linux-fsdevel@vger.kernel.org, linux-cachefs@redhat.com, linux-xfs@vger.kernel.org, linux-mm@kvack.org, Michal Hocko , Christoph Hellwig Subject: Re: [PATCH v13 1/4] mm: Add become_kswapd and restore_kswapd Message-ID: <20201217030609.GP632069@dread.disaster.area> References: <20201217011157.92549-1-laoar.shao@gmail.com> <20201217011157.92549-2-laoar.shao@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201217011157.92549-2-laoar.shao@gmail.com> X-Optus-CM-Score: 0 X-Optus-CM-Analysis: v=2.3 cv=YKPhNiOx c=1 sm=1 tr=0 cx=a_idp_d a=uDU3YIYVKEaHT0eX+MXYOQ==:117 a=uDU3YIYVKEaHT0eX+MXYOQ==:17 a=kj9zAlcOel0A:10 a=zTNgK-yGK50A:10 a=JfrnYn6hAAAA:8 a=7-415B0cAAAA:8 a=iox4zFpeAAAA:8 a=yPCof4ZbAAAA:8 a=pGLkceISAAAA:8 a=4_ML_MP96qNlA5ZoDggA:9 a=CjuIK1q_8ugA:10 a=1CNFftbPRP8L7MoqJWF3:22 a=biEYGPWJfzWAr4FL6Ov7:22 a=WzC6qhA0u3u7Ye7llzcV:22 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Thu, Dec 17, 2020 at 09:11:54AM +0800, Yafang Shao wrote: > From: "Matthew Wilcox (Oracle)" > > Since XFS needs to pretend to be kswapd in some of its worker threads, > create methods to save & restore kswapd state. Don't bother restoring > kswapd state in kswapd -- the only time we reach this code is when we're > exiting and the task_struct is about to be destroyed anyway. > > Cc: Dave Chinner > Acked-by: Michal Hocko > Reviewed-by: Darrick J. Wong > Reviewed-by: Christoph Hellwig > Signed-off-by: Matthew Wilcox (Oracle) > Signed-off-by: Yafang Shao > --- > fs/xfs/libxfs/xfs_btree.c | 14 ++++++++------ > include/linux/sched/mm.h | 23 +++++++++++++++++++++++ > mm/vmscan.c | 16 +--------------- > 3 files changed, 32 insertions(+), 21 deletions(-) > > diff --git a/fs/xfs/libxfs/xfs_btree.c b/fs/xfs/libxfs/xfs_btree.c > index 51dbff9b0908..0f35b7a38e76 100644 > --- a/fs/xfs/libxfs/xfs_btree.c > +++ b/fs/xfs/libxfs/xfs_btree.c > @@ -2813,8 +2813,9 @@ xfs_btree_split_worker( > { > struct xfs_btree_split_args *args = container_of(work, > struct xfs_btree_split_args, work); > + bool is_kswapd = args->kswapd; > unsigned long pflags; > - unsigned long new_pflags = PF_MEMALLOC_NOFS; > + int memalloc_nofs; > > /* > * we are in a transaction context here, but may also be doing work > @@ -2822,16 +2823,17 @@ xfs_btree_split_worker( > * temporarily to ensure that we don't block waiting for memory reclaim > * in any way. > */ > - if (args->kswapd) > - new_pflags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD; > - > - current_set_flags_nested(&pflags, new_pflags); > + if (is_kswapd) > + pflags = become_kswapd(); > + memalloc_nofs = memalloc_nofs_save(); > > args->result = __xfs_btree_split(args->cur, args->level, args->ptrp, > args->key, args->curp, args->stat); > complete(args->done); > > - current_restore_flags_nested(&pflags, new_pflags); > + memalloc_nofs_restore(memalloc_nofs); > + if (is_kswapd) > + restore_kswapd(pflags); > } > > /* > diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h > index d5ece7a9a403..2faf03e79a1e 100644 > --- a/include/linux/sched/mm.h > +++ b/include/linux/sched/mm.h > @@ -278,6 +278,29 @@ static inline void memalloc_nocma_restore(unsigned int flags) > } > #endif > > +/* > + * Tell the memory management code that this thread is working on behalf > + * of background memory reclaim (like kswapd). That means that it will > + * get access to memory reserves should it need to allocate memory in > + * order to make forward progress. With this great power comes great > + * responsibility to not exhaust those reserves. > + */ > +#define KSWAPD_PF_FLAGS (PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD) > + > +static inline unsigned long become_kswapd(void) > +{ > + unsigned long flags = current->flags & KSWAPD_PF_FLAGS; > + > + current->flags |= KSWAPD_PF_FLAGS; > + > + return flags; > +} You can get rid of the empty lines out of this function. > +static inline void restore_kswapd(unsigned long flags) > +{ > + current->flags &= ~(flags ^ KSWAPD_PF_FLAGS); > +} Urk, that requires thinking about to determine whether it is correct. And it is 3 runtime logic operations (^, ~ and &) too. The way all the memalloc_*_restore() functions restore the previous flags is obviously correct and only requires 2 runtime logic operations because the compiler calculates the ~ operation on the constant. So why do it differently here? i.e.: current->flags = (current->flags & ~KSWAPD_PF_FLAGS) | flags; > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -3870,19 +3870,7 @@ static int kswapd(void *p) > if (!cpumask_empty(cpumask)) > set_cpus_allowed_ptr(tsk, cpumask); > > - /* > - * Tell the memory management that we're a "memory allocator", > - * and that if we need more memory we should get access to it > - * regardless (see "__alloc_pages()"). "kswapd" should > - * never get caught in the normal page freeing logic. > - * > - * (Kswapd normally doesn't need memory anyway, but sometimes > - * you need a small amount of memory in order to be able to > - * page out something else, and this flag essentially protects > - * us from recursively trying to free more memory as we're > - * trying to free the first piece of memory in the first place). > - */ > - tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD; > + become_kswapd(); > set_freezable(); > > WRITE_ONCE(pgdat->kswapd_order, 0); > @@ -3932,8 +3920,6 @@ static int kswapd(void *p) > goto kswapd_try_sleep; > } > > - tsk->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD); > - Missing a restore_kswapd()? Cheers, Dave. -- Dave Chinner david@fromorbit.com