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From: Jason Gunthorpe <jgg@ziepe.ca>
To: Jerome Glisse <jglisse@redhat.com>
Cc: "Michal Hocko" <mhocko@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-mm@kvack.org,
	"DRI Development" <dri-devel@lists.freedesktop.org>,
	"Intel Graphics Development" <intel-gfx@lists.freedesktop.org>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"David Rientjes" <rientjes@google.com>,
	"Christian König" <christian.koenig@amd.com>,
	"Masahiro Yamada" <yamada.masahiro@socionext.com>,
	"Wei Wang" <wvw@google.com>,
	"Andy Shevchenko" <andriy.shevchenko@linux.intel.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Jann Horn" <jannh@google.com>, "Feng Tang" <feng.tang@intel.com>,
	"Kees Cook" <keescook@chromium.org>,
	"Randy Dunlap" <rdunlap@infradead.org>,
	"Daniel Vetter" <daniel.vetter@intel.com>
Subject: Re: [PATCH 2/5] kernel.h: Add non_block_start/end()
Date: Thu, 15 Aug 2019 14:17:49 -0300
Message-ID: <20190815171749.GM21596@ziepe.ca> (raw)
In-Reply-To: <20190815171156.GB30916@redhat.com>

On Thu, Aug 15, 2019 at 01:11:56PM -0400, Jerome Glisse wrote:
> On Thu, Aug 15, 2019 at 01:56:31PM -0300, Jason Gunthorpe wrote:
> > On Thu, Aug 15, 2019 at 06:00:41PM +0200, Michal Hocko wrote:
> > 
> > > > AFAIK 'GFP_NOWAIT' is characterized by the lack of __GFP_FS and
> > > > __GFP_DIRECT_RECLAIM..
> > > >
> > > > This matches the existing test in __need_fs_reclaim() - so if you are
> > > > OK with GFP_NOFS, aka __GFP_IO which triggers try_to_compact_pages(),
> > > > allocations during OOM, then I think fs_reclaim already matches what
> > > > you described?
> > > 
> > > No GFP_NOFS is equally bad. Please read my other email explaining what
> > > the oom_reaper actually requires. In short no blocking on direct or
> > > indirect dependecy on memory allocation that might sleep.
> > 
> > It is much easier to follow with some hints on code, so the true
> > requirement is that the OOM repear not block on GFP_FS and GFP_IO
> > allocations, great, that constraint is now clear.
> > 
> > > If you can express that in the existing lockdep machinery. All
> > > fine. But then consider deployments where lockdep is no-no because
> > > of the overhead.
> > 
> > This is all for driver debugging. The point of lockdep is to find all
> > these paths without have to hit them as actual races, using debug
> > kernels.
> > 
> > I don't think we need this kind of debugging on production kernels?
> > 
> > > > The best we got was drivers tested the VA range and returned success
> > > > if they had no interest. Which is a big win to be sure, but it looks
> > > > like getting any more is not really posssible.
> > > 
> > > And that is already a great win! Because many notifiers only do care
> > > about particular mappings. Please note that backing off unconditioanlly
> > > will simply cause that the oom reaper will have to back off not doing
> > > any tear down anything.
> > 
> > Well, I'm working to propose that we do the VA range test under core
> > mmu notifier code that cannot block and then we simply remove the idea
> > of blockable from drivers using this new 'range notifier'. 
> > 
> > I think this pretty much solves the concern?
> 
> I am not sure i follow what you propose here ? Like i pointed out in
> another email for GPU we do need to be able to sleep (we might get
> lucky and not need too but this is runtime thing) within notifier
> range_start callback. This has been something allow by notifier since
> it has been introduced in the kernel.

Sorry, I mean remove the idea of the blockable flag from the
drivers. Drivers will always be able to block, within the existing
limitation of fs_reclaim

Jason


  reply index

Thread overview: 69+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-14 20:20 [PATCH 0/5] hmm & mmu_notifier debug/lockdep annotations Daniel Vetter
2019-08-14 20:20 ` [PATCH 1/5] mm: Check if mmu notifier callbacks are allowed to fail Daniel Vetter
2019-08-14 22:14   ` Andrew Morton
2019-08-14 23:22     ` Jason Gunthorpe
2019-08-14 23:34     ` Ralph Campbell
2019-08-16 17:19   ` Jason Gunthorpe
2019-08-14 20:20 ` [PATCH 2/5] kernel.h: Add non_block_start/end() Daniel Vetter
2019-08-14 20:45   ` Andrew Morton
2019-08-15  6:52     ` Daniel Vetter
2019-08-15  8:44     ` Michal Hocko
2019-08-15 13:04       ` Jason Gunthorpe
2019-08-15 13:12         ` Daniel Vetter
2019-08-15 14:37           ` Jason Gunthorpe
2019-08-15 14:43             ` Daniel Vetter
2019-08-15 15:10               ` Jason Gunthorpe
2019-08-15 16:25                 ` Daniel Vetter
2019-08-15 17:35                   ` Jason Gunthorpe
2019-08-15 17:39                     ` Jerome Glisse
2019-08-15 18:01                       ` Jason Gunthorpe
2019-08-15 18:27                         ` Jerome Glisse
2019-08-15 18:57                           ` Jason Gunthorpe
2019-08-15 16:32                 ` Jerome Glisse
2019-08-15 17:16                   ` Jason Gunthorpe
2019-08-15 17:21                     ` Daniel Vetter
2019-08-15 17:35                       ` Jerome Glisse
2019-08-15 13:24         ` Michal Hocko
2019-08-15 22:15       ` Andrew Morton
2019-08-16  8:24         ` Michal Hocko
2019-08-14 23:58   ` Jason Gunthorpe
2019-08-15  6:58     ` Daniel Vetter
2019-08-15 12:23       ` Jason Gunthorpe
2019-08-15 13:21         ` Michal Hocko
2019-08-15 14:12           ` Jason Gunthorpe
2019-08-15 16:00             ` Michal Hocko
2019-08-15 16:56               ` Jason Gunthorpe
2019-08-15 17:11                 ` Jerome Glisse
2019-08-15 17:17                   ` Jason Gunthorpe [this message]
2019-08-15 17:42                 ` Michal Hocko
2019-08-15 17:57                   ` Jerome Glisse
2019-08-15 18:24                   ` Jason Gunthorpe
2019-08-15 19:05                     ` Michal Hocko
2019-08-15 19:18                       ` Jason Gunthorpe
2019-08-15 19:35                         ` Michal Hocko
2019-08-15 20:13                           ` Jason Gunthorpe
2019-08-16  8:10                             ` Michal Hocko
2019-08-16 12:19                               ` Jason Gunthorpe
2019-08-16 12:26                                 ` Michal Hocko
2019-08-15 20:16                           ` [Intel-gfx] " Daniel Vetter
2019-08-15 20:27                             ` Jason Gunthorpe
2019-08-15 20:49                               ` Daniel Vetter
2019-08-16  1:00                                 ` Jason Gunthorpe
2019-08-16  6:20                                   ` Daniel Vetter
2019-08-16 12:12                                     ` Jason Gunthorpe
2019-08-16 14:11                                       ` Daniel Vetter
2019-08-16 14:38                                         ` Jason Gunthorpe
2019-08-16 16:36                                           ` Daniel Vetter
2019-08-16 16:54                                             ` Jason Gunthorpe
2019-08-16  8:27                             ` Michal Hocko
2019-08-14 20:20 ` [PATCH 3/5] mm, notifier: Catch sleeping/blocking for !blockable Daniel Vetter
2019-08-15  0:00   ` Jason Gunthorpe
2019-08-15  7:02     ` Daniel Vetter
     [not found]       ` <20190815123556.GB21596@ziepe.ca>
2019-08-17 16:09         ` Daniel Vetter
2019-08-14 20:20 ` [PATCH 4/5] mm, notifier: Add a lockdep map for invalidate_range_start Daniel Vetter
2019-08-15  0:09   ` Jason Gunthorpe
2019-08-15  7:10     ` Daniel Vetter
2019-08-15 12:53       ` Jason Gunthorpe
2019-08-14 20:20 ` [PATCH 5/5] mm/hmm: WARN on illegal ->sync_cpu_device_pagetables errors Daniel Vetter
2019-08-15  0:11   ` Jason Gunthorpe
2019-08-15  7:14     ` Daniel Vetter

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