From: Jason Gunthorpe <jgg@ziepe.ca>
To: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: "DRI Development" <dri-devel@lists.freedesktop.org>,
"Intel Graphics Development" <intel-gfx@lists.freedesktop.org>,
linux-mm@kvack.org, linux-xfs@vger.kernel.org,
linux-fsdevel@vger.kernel.org,
LKML <linux-kernel@vger.kernel.org>,
"Dave Chinner" <david@fromorbit.com>, "Qian Cai" <cai@lca.pw>,
"Thomas Hellström" <thomas_os@shipmail.org>,
"Andrew Morton" <akpm@linux-foundation.org>,
linux-rdma@vger.kernel.org,
"Maarten Lankhorst" <maarten.lankhorst@linux.intel.com>,
"Christian König" <christian.koenig@amd.com>,
"Matthew Wilcox (Oracle)" <willy@infradead.org>,
"Daniel Vetter" <daniel.vetter@intel.com>
Subject: Re: [PATCH 1/3] mm: Track mmu notifiers in fs_reclaim_acquire/release
Date: Fri, 20 Nov 2020 14:23:16 -0400 [thread overview]
Message-ID: <20201120182316.GP244516@ziepe.ca> (raw)
In-Reply-To: <20201120095445.1195585-2-daniel.vetter@ffwll.ch>
On Fri, Nov 20, 2020 at 10:54:42AM +0100, 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
>
> v3: Unbreak the PF_MEMALLOC_ context flags. Thanks to Qian for the
> report and Dave for explaining what I failed to see.
>
> Cc: linux-fsdevel@vger.kernel.org
> Cc: Dave Chinner <david@fromorbit.com>
> Cc: Qian Cai <cai@lca.pw>
> Cc: linux-xfs@vger.kernel.org
> Cc: Thomas Hellström (Intel) <thomas_os@shipmail.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Jason Gunthorpe <jgg@mellanox.com>
> Cc: linux-mm@kvack.org
> Cc: linux-rdma@vger.kernel.org
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Christian König <christian.koenig@amd.com>
> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> ---
> mm/mmu_notifier.c | 7 -------
> mm/page_alloc.c | 31 ++++++++++++++++++++-----------
> 2 files changed, 20 insertions(+), 18 deletions(-)
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Jason
next prev parent reply other threads:[~2020-11-20 18:23 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-20 9:54 [PATCH 0/3] mmu_notifier fs fs_reclaim lockdep annotations Daniel Vetter
2020-11-20 9:54 ` [PATCH 1/3] mm: Track mmu notifiers in fs_reclaim_acquire/release Daniel Vetter
2020-11-20 18:23 ` Jason Gunthorpe [this message]
2020-11-20 9:54 ` [PATCH 2/3] mm: Extract might_alloc() debug check Daniel Vetter
2020-11-20 17:19 ` Randy Dunlap
2020-11-20 17:31 ` Daniel Vetter
2020-11-20 18:07 ` Jason Gunthorpe
2020-11-24 14:34 ` Daniel Vetter
2020-11-24 15:27 ` Jason Gunthorpe
2020-11-20 9:54 ` [PATCH 3/3] locking/selftests: Add testcases for fs_reclaim Daniel Vetter
2020-11-20 12:31 ` Peter Zijlstra
2020-11-20 9:54 ` [PATCH] drm/ttm: don't set page->mapping Daniel Vetter
2020-11-20 10:04 ` Christian König
2020-11-20 10:05 ` Daniel Vetter
2020-11-20 10:08 ` Christian König
2020-11-20 15:01 ` Daniel Vetter
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