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Sun, 21 Jun 2020 13:01:05 -0700 (PDT) Date: Sun, 21 Jun 2020 22:01:03 +0200 From: Daniel Vetter To: Qian Cai Subject: Re: [PATCH] mm: Track mmu notifiers in fs_reclaim_acquire/release Message-ID: <20200621200103.GV20149@phenom.ffwll.local> Mail-Followup-To: Qian Cai , Intel Graphics Development , DRI Development , LKML , amd-gfx list , Thomas =?iso-8859-1?Q?Hellstr=F6m?= , Andrew Morton , Jason Gunthorpe , Linux MM , linux-rdma , Maarten Lankhorst , Christian =?iso-8859-1?Q?K=F6nig?= , Daniel Vetter , linux-xfs@vger.kernel.org References: <20200604081224.863494-2-daniel.vetter@ffwll.ch> <20200610194101.1668038-1-daniel.vetter@ffwll.ch> <20200621174205.GB1398@lca.pw> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-Operating-System: Linux phenom 5.6.0-1-amd64 X-BeenThere: amd-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Discussion list for AMD gfx List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-rdma , Intel Graphics Development , Maarten Lankhorst , LKML , amd-gfx list , Christian =?iso-8859-1?Q?K=F6nig?= , linux-xfs@vger.kernel.org, Linux MM , Jason Gunthorpe , DRI Development , Daniel Vetter , Andrew Morton , Thomas =?iso-8859-1?Q?Hellstr=F6m?= Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Errors-To: amd-gfx-bounces@lists.freedesktop.org Sender: "amd-gfx" On Sun, Jun 21, 2020 at 08:07:08PM +0200, Daniel Vetter wrote: > On Sun, Jun 21, 2020 at 7:42 PM Qian Cai wrote: > > > > On Wed, Jun 10, 2020 at 09:41:01PM +0200, Daniel Vetter wrote: > > > fs_reclaim_acquire/release nicely catch recursion issues when > > > allocating GFP_KERNEL memory against shrinkers (which gpu drivers tend > > > to use to keep the excessive caches in check). For mmu notifier > > > recursions we do have lockdep annotations since 23b68395c7c7 > > > ("mm/mmu_notifiers: add a lockdep map for invalidate_range_start/end"= ). > > > > > > But these only fire if a path actually results in some pte > > > invalidation - for most small allocations that's very rarely the case. > > > The other trouble is that pte invalidation can happen any time when > > > __GFP_RECLAIM is set. Which means only really GFP_ATOMIC is a safe > > > choice, GFP_NOIO isn't good enough to avoid potential mmu notifier > > > recursion. > > > > > > I was pondering whether we should just do the general annotation, but > > > there's always the risk for false positives. Plus I'm assuming that > > > the core fs and io code is a lot better reviewed and tested than > > > random mmu notifier code in drivers. Hence why I decide to only > > > annotate for that specific case. > > > > > > Furthermore even if we'd create a lockdep map for direct reclaim, we'd > > > still need to explicit pull in the mmu notifier map - there's a lot > > > more places that do pte invalidation than just direct reclaim, these > > > two contexts arent the same. > > > > > > Note that the mmu notifiers needing their own independent lockdep map > > > is also the reason we can't hold them from fs_reclaim_acquire to > > > fs_reclaim_release - it would nest with the acquistion in the pte > > > invalidation code, causing a lockdep splat. And we can't remove the > > > annotations from pte invalidation and all the other places since > > > they're called from many other places than page reclaim. Hence we can > > > only do the equivalent of might_lock, but on the raw lockdep map. > > > > > > With this we can also remove the lockdep priming added in 66204f1d2d1b > > > ("mm/mmu_notifiers: prime lockdep") since the new annotations are > > > strictly more powerful. > > > > > > v2: Review from Thomas Hellstrom: > > > - unbotch the fs_reclaim context check, I accidentally inverted it, > > > but it didn't blow up because I inverted it immediately > > > - fix compiling for !CONFIG_MMU_NOTIFIER > > > > > > Cc: Thomas Hellstr=F6m (Intel) > > > Cc: Andrew Morton > > > Cc: Jason Gunthorpe > > > Cc: linux-mm@kvack.org > > > Cc: linux-rdma@vger.kernel.org > > > Cc: Maarten Lankhorst > > > Cc: Christian K=F6nig > > > Signed-off-by: Daniel Vetter > > > > Replying the right patch here... > > > > Reverting this commit [1] fixed the lockdep warning below while applying > > some memory pressure. > > > > [1] linux-next cbf7c9d86d75 ("mm: track mmu notifiers in fs_reclaim_acq= uire/release") > = > Hm, then I'm confused because > - there's not mmut notifier lockdep map in the splat at a.. > - the patch is supposed to not change anything for fs_reclaim (but the > interim version got that wrong) > - looking at the paths it's kmalloc vs kswapd, both places I totally > expect fs_reflaim to be used. > = > But you're claiming reverting this prevents the lockdep splat. If > that's right, then my reasoning above is broken somewhere. Someone > less blind than me having an idea? > = > Aside this is the first email I've typed, until I realized the first > report was against the broken patch and that looked like a much more > reasonable explanation (but didn't quite match up with the code > paths). Below diff should undo the functional change in my patch. Can you pls test whether the lockdep splat is really gone with that? Might need a lot of testing and memory pressure to be sure, since all these reclaim paths aren't very deterministic. -Daniel --- diff --git a/mm/page_alloc.c b/mm/page_alloc.c index d807587c9ae6..27ea763c6155 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -4191,11 +4191,6 @@ void fs_reclaim_acquire(gfp_t gfp_mask) if (gfp_mask & __GFP_FS) __fs_reclaim_acquire(); = -#ifdef CONFIG_MMU_NOTIFIER - lock_map_acquire(&__mmu_notifier_invalidate_range_start_map); - lock_map_release(&__mmu_notifier_invalidate_range_start_map); -#endif - } } EXPORT_SYMBOL_GPL(fs_reclaim_acquire); -- = Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ amd-gfx mailing list amd-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/amd-gfx