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From: David Hildenbrand <david@redhat.com>
To: Mike Rapoport <rppt@kernel.org>
Cc: David Hildenbrand <david@redhat.com>,
	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>,
	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>,
	Matthew Wilcox <willy@infradead.org>,
	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@vger.kernel.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
	linux-nvdimm@lists.01.org, linux-riscv@lists.infradead.org,
	x86@kernel.org
Subject: Re: [PATCH v8 2/9] mmap: make mlock_future_check() global
Date: Thu, 12 Nov 2020 21:15:18 +0100
Message-ID: <7A16CA44-782D-4ABA-8D93-76BDD0A90F94@redhat.com> (raw)
In-Reply-To: <20201112190827.GP4758@kernel.org>


> Am 12.11.2020 um 20:08 schrieb Mike Rapoport <rppt@kernel.org>:
> 
> On Thu, Nov 12, 2020 at 05:22:00PM +0100, David Hildenbrand wrote:
>>> On 10.11.20 19:06, Mike Rapoport wrote:
>>> On Tue, Nov 10, 2020 at 06:17:26PM +0100, David Hildenbrand wrote:
>>>> On 10.11.20 16:14, Mike Rapoport wrote:
>>>>> From: Mike Rapoport <rppt@linux.ibm.com>
>>>>> 
>>>>> It will be used by the upcoming secret memory implementation.
>>>>> 
>>>>> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
>>>>> ---
>>>>>   mm/internal.h | 3 +++
>>>>>   mm/mmap.c     | 5 ++---
>>>>>   2 files changed, 5 insertions(+), 3 deletions(-)
>>>>> 
>>>>> diff --git a/mm/internal.h b/mm/internal.h
>>>>> index c43ccdddb0f6..ae146a260b14 100644
>>>>> --- a/mm/internal.h
>>>>> +++ b/mm/internal.h
>>>>> @@ -348,6 +348,9 @@ static inline void munlock_vma_pages_all(struct vm_area_struct *vma)
>>>>>   extern void mlock_vma_page(struct page *page);
>>>>>   extern unsigned int munlock_vma_page(struct page *page);
>>>>> +extern int mlock_future_check(struct mm_struct *mm, unsigned long flags,
>>>>> +                  unsigned long len);
>>>>> +
>>>>>   /*
>>>>>    * Clear the page's PageMlocked().  This can be useful in a situation where
>>>>>    * we want to unconditionally remove a page from the pagecache -- e.g.,
>>>>> diff --git a/mm/mmap.c b/mm/mmap.c
>>>>> index 61f72b09d990..c481f088bd50 100644
>>>>> --- a/mm/mmap.c
>>>>> +++ b/mm/mmap.c
>>>>> @@ -1348,9 +1348,8 @@ static inline unsigned long round_hint_to_min(unsigned long hint)
>>>>>       return hint;
>>>>>   }
>>>>> -static inline int mlock_future_check(struct mm_struct *mm,
>>>>> -                     unsigned long flags,
>>>>> -                     unsigned long len)
>>>>> +int mlock_future_check(struct mm_struct *mm, unsigned long flags,
>>>>> +               unsigned long len)
>>>>>   {
>>>>>       unsigned long locked, lock_limit;
>>>>> 
>>>> 
>>>> So, an interesting question is if you actually want to charge secretmem
>>>> pages against mlock now, or if you want a dedicated secretmem cgroup
>>>> controller instead?
>>> 
>>> Well, with the current implementation there are three limits an
>>> administrator can use to control secretmem limits: mlock, memcg and
>>> kernel parameter.
>>> 
>>> The kernel parameter puts a global upper limit for secretmem usage,
>>> memcg accounts all secretmem allocations, including the unused memory in
>>> large pages caching and mlock allows per task limit for secretmem
>>> mappings, well, like mlock does.
>>> 
>>> I didn't consider a dedicated cgroup, as it seems we already have enough
>>> existing knobs and a new one would be unnecessary.
>> 
>> To me it feels like the mlock() limit is a wrong fit for secretmem. But
>> maybe there are other cases of using the mlock() limit without actually
>> doing mlock() that I am not aware of (most probably :) )?
> 
> Secretmem does not explicitly calls to mlock() but it does what mlock()
> does and a bit more. Citing mlock(2):
> 
>  mlock(),  mlock2(),  and  mlockall()  lock  part  or all of the calling
>  process's virtual address space into RAM, preventing that  memory  from
>  being paged to the swap area.
> 
> So, based on that secretmem pages are not swappable, I think that
> RLIMIT_MEMLOCK is appropriate here.
> 

The page explicitly lists mlock() system calls. E.g., we also don‘t account for gigantic pages - which might be allocated from CMA and are not swappable.



>> I mean, my concern is not earth shattering, this can be reworked later. As I
>> said, it just feels wrong.
>> 
>> -- 
>> Thanks,
>> 
>> David / dhildenb
>> 
> 
> -- 
> Sincerely yours,
> Mike.
> 


  reply index

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-10 15:14 [PATCH v8 0/9] mm: introduce memfd_secret system call to create "secret" memory areas Mike Rapoport
2020-11-10 15:14 ` [PATCH v8 1/9] mm: add definition of PMD_PAGE_ORDER Mike Rapoport
2020-11-10 15:14 ` [PATCH v8 2/9] mmap: make mlock_future_check() global Mike Rapoport
2020-11-10 17:17   ` David Hildenbrand
2020-11-10 18:06     ` Mike Rapoport
2020-11-12 16:22       ` David Hildenbrand
2020-11-12 19:08         ` Mike Rapoport
2020-11-12 20:15           ` David Hildenbrand [this message]
2020-11-15  8:26             ` Mike Rapoport
2020-11-17 15:09               ` David Hildenbrand
2020-11-17 15:58                 ` Mike Rapoport
2020-11-10 15:14 ` [PATCH v8 3/9] set_memory: allow set_direct_map_*_noflush() for multiple pages Mike Rapoport
2020-11-13 12:26   ` Catalin Marinas
2020-11-10 15:14 ` [PATCH v8 4/9] mm: introduce memfd_secret system call to create "secret" memory areas Mike Rapoport
2020-11-13 13:58   ` Matthew Wilcox
2020-11-15  8:53     ` Mike Rapoport
2020-11-13 14:06   ` Matthew Wilcox
2020-11-15  8:45     ` Mike Rapoport
2020-11-10 15:14 ` [PATCH v8 5/9] secretmem: use PMD-size pages to amortize direct map fragmentation Mike Rapoport
2020-11-10 15:14 ` [PATCH v8 6/9] secretmem: add memcg accounting Mike Rapoport
2020-11-13  1:35   ` Andrew Morton
2020-11-13 23:42   ` Roman Gushchin
2020-11-15  9:17     ` Mike Rapoport
2020-11-10 15:14 ` [PATCH v8 7/9] PM: hibernate: disable when there are active secretmem users Mike Rapoport
2020-11-10 15:14 ` [PATCH v8 8/9] arch, mm: wire up memfd_secret system call were relevant Mike Rapoport
2020-11-13 12:25   ` Catalin Marinas
2020-11-15  8:56     ` Mike Rapoport
2020-11-10 15:14 ` [PATCH v8 9/9] secretmem: test: add basic selftest for memfd_secret(2) Mike Rapoport
2020-11-12 14:56 ` [PATCH v8 0/9] mm: introduce memfd_secret system call to create "secret" memory areas Mike Rapoport

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