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Date: Sun, 15 Nov 2020 10:26:25 +0200
From: Mike Rapoport <rppt@...nel.org>
To: David Hildenbrand <david@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Alexander Viro <viro@...iv.linux.org.uk>,
Andy Lutomirski <luto@...nel.org>,
Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
Catalin Marinas <catalin.marinas@....com>,
Christopher Lameter <cl@...ux.com>,
Dan Williams <dan.j.williams@...el.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Elena Reshetova <elena.reshetova@...el.com>,
"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
James Bottomley <jejb@...ux.ibm.com>,
"Kirill A. Shutemov" <kirill@...temov.name>,
Matthew Wilcox <willy@...radead.org>,
Mark Rutland <mark.rutland@....com>,
Mike Rapoport <rppt@...ux.ibm.com>,
Michael Kerrisk <mtk.manpages@...il.com>,
Palmer Dabbelt <palmer@...belt.com>,
Paul Walmsley <paul.walmsley@...ive.com>,
Peter Zijlstra <peterz@...radead.org>,
Rick Edgecombe <rick.p.edgecombe@...el.com>,
Shuah Khan <shuah@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Tycho Andersen <tycho@...ho.ws>, Will Deacon <will@...nel.org>,
linux-api@...r.kernel.org, linux-arch@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org,
linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
linux-nvdimm@...ts.01.org, linux-riscv@...ts.infradead.org,
x86@...nel.org
Subject: Re: [PATCH v8 2/9] mmap: make mlock_future_check() global
On Thu, Nov 12, 2020 at 09:15:18PM +0100, David Hildenbrand wrote:
>
> > Am 12.11.2020 um 20:08 schrieb Mike Rapoport <rppt@...nel.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@...ux.ibm.com>
> >>>>>
> >>>>> It will be used by the upcoming secret memory implementation.
> >>>>>
> >>>>> Signed-off-by: Mike Rapoport <rppt@...ux.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.
Well, it's mlock() man page, isn't it? ;-)
My thinking was that since secretmem does what mlock() does wrt
swapability, it should at least obey the same limit, i.e.
RLIMIT_MEMLOCK.
> E.g., we also don‘t
> account for gigantic pages - which might be allocated from CMA and are
> not swappable.
Do you mean gigantic pages in hugetlbfs?
It seems to me that hugetlbfs accounting is a completely different
story.
> >> 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.
> >
>
--
Sincerely yours,
Mike.
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