From: Shakeel Butt <shakeelb@google.com>
To: Michal Hocko <mhocko@suse.com>
Cc: Roman Gushchin <guro@fb.com>,
Matthew Wilcox <willy@infradead.org>,
Mike Rapoport <rppt@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Andy Lutomirski <luto@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
Borislav Petkov <bp@alien8.de>,
Catalin Marinas <catalin.marinas@arm.com>,
Christopher Lameter <cl@linux.com>,
Dan Williams <dan.j.williams@intel.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
David Hildenbrand <david@redhat.com>,
Elena Reshetova <elena.reshetova@intel.com>,
"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
James Bottomley <jejb@linux.ibm.com>,
"Kirill A. Shutemov" <kirill@shutemov.name>,
Mark Rutland <mark.rutland@arm.com>,
Mike Rapoport <rppt@linux.ibm.com>,
Michael Kerrisk <mtk.manpages@gmail.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Paul Walmsley <paul.walmsley@sifive.com>,
Peter Zijlstra <peterz@infradead.org>,
Rick Edgecombe <rick.p.edgecombe@intel.com>,
Shuah Khan <shuah@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Tycho Andersen <tycho@tycho.ws>, Will Deacon <will@kernel.org>,
linux-api@vger.kernel.org, linux-arch@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
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LKML <linux-kernel@vger.kernel.org>,
linux-kselftest@vger.kernel.org, linux-nvdimm@lists.01.org,
linux-riscv@lists.infradead.org, x86@kernel.org,
Hagen Paul Pfeifer <hagen@jauu.net>,
Palmer Dabbelt <palmerdabbelt@google.com>
Subject: Re: [PATCH v16 08/11] secretmem: add memcg accounting
Date: Thu, 28 Jan 2021 06:57:31 -0800 [thread overview]
Message-ID: <CALvZod4G3ipt84pQVHYT921hmXQTswivcrU0iqpTof4tO91GxA@mail.gmail.com> (raw)
In-Reply-To: <YBLInhns9ysc4wNF@dhcp22.suse.cz>
On Thu, Jan 28, 2021 at 6:22 AM Michal Hocko <mhocko@suse.com> wrote:
>
> On Thu 28-01-21 06:05:11, Shakeel Butt wrote:
> > On Wed, Jan 27, 2021 at 11:59 PM Michal Hocko <mhocko@suse.com> wrote:
> > >
> > > On Wed 27-01-21 10:42:13, Roman Gushchin wrote:
> > > > On Tue, Jan 26, 2021 at 04:05:55PM +0100, Michal Hocko wrote:
> > > > > On Tue 26-01-21 14:48:38, Matthew Wilcox wrote:
> > > > > > On Mon, Jan 25, 2021 at 11:38:17PM +0200, Mike Rapoport wrote:
> > > > > > > I cannot use __GFP_ACCOUNT because cma_alloc() does not use gfp.
> > > > > > > Besides, kmem accounting with __GFP_ACCOUNT does not seem
> > > > > > > to update stats and there was an explicit request for statistics:
> > > > > > >
> > > > > > > https://lore.kernel.org/lkml/CALo0P13aq3GsONnZrksZNU9RtfhMsZXGWhK1n=xYJWQizCd4Zw@mail.gmail.com/
> > > > > > >
> > > > > > > As for (ab)using NR_SLAB_UNRECLAIMABLE_B, as it was already discussed here:
> > > > > > >
> > > > > > > https://lore.kernel.org/lkml/20201129172625.GD557259@kernel.org/
> > > > > > >
> > > > > > > I think that a dedicated stats counter would be too much at the moment and
> > > > > > > NR_SLAB_UNRECLAIMABLE_B is the only explicit stat for unreclaimable memory.
> > > > > >
> > > > > > That's not true -- Mlocked is also unreclaimable. And doesn't this
> > > > > > feel more like mlocked memory than unreclaimable slab? It's also
> > > > > > Unevictable, so could be counted there instead.
> > > > >
> > > > > yes, that is indeed true, except the unreclaimable counter is tracking
> > > > > the unevictable LRUs. These pages are not on any LRU and that can cause
> > > > > some confusion. Maybe they shouldn't be so special and they should live
> > > > > on unevistable LRU and get their stats automagically.
> > > > >
> > > > > I definitely do agree that this would be a better fit than NR_SLAB
> > > > > abuse. But considering that this is somehow even more special than mlock
> > > > > then a dedicated counter sounds as even better fit.
> > > >
> > > > I think it depends on how large these areas will be in practice.
> > > > If they will be measured in single or double digits MBs, a separate entry
> > > > is hardly a good choice: because of the batching the displayed value
> > > > will be in the noise range, plus every new vmstat item adds to the
> > > > struct mem_cgroup size.
> > > >
> > > > If it will be measured in GBs, of course, a separate counter is preferred.
> > > > So I'd suggest to go with NR_SLAB (which should have been named NR_KMEM)
> > > > as now and conditionally switch to a separate counter later.
> > >
> > > I really do not think the overall usage matters when it comes to abusing
> > > other counters. Changing this in future will be always tricky and there
> > > always be our favorite "Can this break userspace" question. Yes we dared
> > > to change meaning of some counters but this is not generally possible.
> > > Just have a look how accounting shmem as a page cache has turned out
> > > being much more tricky than many like.
> > >
> > > Really if a separate counter is a big deal, for which I do not see any
> > > big reason, then this should be accounted as unevictable (as suggested
> > > by Matthew) and ideally pages of those mappings should be sitting in the
> > > unevictable LRU as well unless there is a strong reason against.
> > >
> >
> > Why not decide based on the movability of these pages? If movable then
> > unevictable LRU seems like the right way otherwise NR_SLAB.
>
> I really do not follow. If the page is unevictable then why movability
> matters?
My point was if these pages are very much similar to our existing
definition of unevictable LRU pages then it makes more sense to
account for these pages into unevictable stat.
> I also fail to see why NR_SLAB is even considered considering
> this is completely outside of slab proper.
>
> Really what is the point? What are we trying to achieve by stats? Do we
> want to know how much secret memory is used because that is an
> interesting/important information or do we just want to make some
> accounting?
>
> Just think at it from a practical point of view. I want to know how much
> slab memory is used because it can give me an idea whether kernel is
> consuming unexpected amount of memory. Now I have to subtract _some_
> number to get that information. Where do I get that some number?
>
> We have been creative with counters and it tends to kick back much more
> often than it helps.
>
> I really do not want this to turn into an endless bike shed but either
> this should be accounted as a general type of memory (unevictable would
> be a good fit because that is a userspace memory which is not
> reclaimable) or it needs its own counter to tell how much of this
> specific type of memory is used for this purpose.
>
I suggested having a separate counter in the previous version but got
shot down based on the not-yet-clear benefit of a separate stat for
it.
There is also an option to not add new or use existing stat at this
moment. As there will be more clear use-cases and usage of secretmem,
adding a new stat at that time would be much simpler than changing the
definition of existing stats.
next prev parent reply other threads:[~2021-01-28 14:57 UTC|newest]
Thread overview: 78+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-21 12:27 [PATCH v16 00/11] mm: introduce memfd_secret system call to create "secret" memory areas Mike Rapoport
2021-01-21 12:27 ` [PATCH v16 01/11] mm: add definition of PMD_PAGE_ORDER Mike Rapoport
2021-01-21 12:27 ` [PATCH v16 02/11] mmap: make mlock_future_check() global Mike Rapoport
2021-01-21 12:27 ` [PATCH v16 03/11] riscv/Kconfig: make direct map manipulation options depend on MMU Mike Rapoport
2021-01-21 12:27 ` [PATCH v16 04/11] set_memory: allow set_direct_map_*_noflush() for multiple pages Mike Rapoport
2021-01-21 12:27 ` [PATCH v16 05/11] set_memory: allow querying whether set_direct_map_*() is actually enabled Mike Rapoport
2021-01-21 12:27 ` [PATCH v16 06/11] mm: introduce memfd_secret system call to create "secret" memory areas Mike Rapoport
2021-01-25 17:01 ` Michal Hocko
2021-01-25 21:36 ` Mike Rapoport
2021-01-26 7:16 ` Michal Hocko
2021-01-26 8:33 ` Mike Rapoport
2021-01-26 9:00 ` Michal Hocko
2021-01-26 9:20 ` Mike Rapoport
2021-01-26 9:49 ` Michal Hocko
2021-01-26 9:53 ` David Hildenbrand
2021-01-26 10:19 ` Michal Hocko
2021-01-26 9:20 ` Michal Hocko
2021-02-03 12:15 ` Michal Hocko
2021-02-04 11:34 ` Mike Rapoport
2021-01-21 12:27 ` [PATCH v16 07/11] secretmem: use PMD-size pages to amortize direct map fragmentation Mike Rapoport
2021-01-26 11:46 ` Michal Hocko
2021-01-26 11:56 ` David Hildenbrand
2021-01-26 12:08 ` Michal Hocko
2021-01-28 9:22 ` Mike Rapoport
2021-01-28 13:01 ` Michal Hocko
2021-01-28 13:28 ` Christoph Lameter
2021-01-28 13:49 ` Michal Hocko
2021-01-28 15:56 ` Christoph Lameter
2021-01-28 16:23 ` Michal Hocko
2021-01-28 15:28 ` James Bottomley
2021-01-29 7:03 ` Mike Rapoport
2021-01-28 21:05 ` James Bottomley
2021-01-29 7:53 ` Michal Hocko
2021-01-29 8:23 ` Michal Hocko
2021-02-01 16:56 ` James Bottomley
2021-02-02 9:35 ` Michal Hocko
2021-02-02 12:48 ` Mike Rapoport
2021-02-02 13:14 ` David Hildenbrand
2021-02-02 13:32 ` Michal Hocko
2021-02-02 14:12 ` David Hildenbrand
2021-02-02 14:22 ` Michal Hocko
2021-02-02 14:26 ` David Hildenbrand
2021-02-02 14:32 ` Michal Hocko
2021-02-02 14:34 ` David Hildenbrand
2021-02-02 18:15 ` Mike Rapoport
2021-02-02 18:55 ` James Bottomley
2021-02-03 12:09 ` Michal Hocko
2021-02-04 11:31 ` Mike Rapoport
2021-02-02 13:27 ` Michal Hocko
2021-02-02 19:10 ` Mike Rapoport
2021-02-03 9:12 ` Michal Hocko
2021-02-04 9:58 ` Mike Rapoport
2021-02-04 13:02 ` Michal Hocko
2021-01-29 7:21 ` Mike Rapoport
2021-01-29 8:51 ` Michal Hocko
2021-02-02 14:42 ` David Hildenbrand
2021-01-21 12:27 ` [PATCH v16 08/11] secretmem: add memcg accounting Mike Rapoport
2021-01-25 16:17 ` Matthew Wilcox
2021-01-25 17:18 ` Shakeel Butt
2021-01-25 21:35 ` Mike Rapoport
2021-01-28 15:07 ` Shakeel Butt
2021-01-25 16:54 ` Michal Hocko
2021-01-25 21:38 ` Mike Rapoport
2021-01-26 7:31 ` Michal Hocko
2021-01-26 8:56 ` Mike Rapoport
2021-01-26 9:15 ` Michal Hocko
2021-01-26 14:48 ` Matthew Wilcox
2021-01-26 15:05 ` Michal Hocko
2021-01-27 18:42 ` Roman Gushchin
2021-01-28 7:58 ` Michal Hocko
2021-01-28 14:05 ` Shakeel Butt
2021-01-28 14:22 ` Michal Hocko
2021-01-28 14:57 ` Shakeel Butt [this message]
2021-01-21 12:27 ` [PATCH v16 09/11] PM: hibernate: disable when there are active secretmem users Mike Rapoport
2021-01-21 12:27 ` [PATCH v16 10/11] arch, mm: wire up memfd_secret system call where relevant Mike Rapoport
2021-01-25 18:18 ` Catalin Marinas
2021-01-21 12:27 ` [PATCH v16 11/11] secretmem: test: add basic selftest for memfd_secret(2) Mike Rapoport
2021-01-21 22:18 ` [PATCH v16 00/11] mm: introduce memfd_secret system call to create "secret" memory areas Andrew Morton
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