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[91.12.99.29]) by smtp.gmail.com with ESMTPSA id 35sm8578483wro.71.2020.11.12.12.15.19 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 12 Nov 2020 12:15:19 -0800 (PST) Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable From: David Hildenbrand Mime-Version: 1.0 (1.0) 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> References: <20201112190827.GP4758@kernel.org> Cc: David Hildenbrand , Andrew Morton , Alexander Viro , Andy Lutomirski , Arnd Bergmann , Borislav Petkov , Catalin Marinas , Christopher Lameter , Dan Williams , Dave Hansen , Elena Reshetova , "H. Peter Anvin" , Ingo Molnar , James Bottomley , "Kirill A. Shutemov" , Matthew Wilcox , Mark Rutland , Mike Rapoport , Michael Kerrisk , Palmer Dabbelt , Paul Walmsley , Peter Zijlstra , Rick Edgecombe , Shuah Khan , Thomas Gleixner , Tycho Andersen , Will Deacon , 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 In-Reply-To: <20201112190827.GP4758@kernel.org> To: Mike Rapoport X-Mailer: iPhone Mail (18A8395) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > Am 12.11.2020 um 20:08 schrieb Mike Rapoport : >=20 > =EF=BB=BFOn 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 >>>>>=20 >>>>> It will be used by the upcoming secret memory implementation. >>>>>=20 >>>>> Signed-off-by: Mike Rapoport >>>>> --- >>>>> mm/internal.h | 3 +++ >>>>> mm/mmap.c | 5 ++--- >>>>> 2 files changed, 5 insertions(+), 3 deletions(-) >>>>>=20 >>>>> 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 fla= gs, >>>>> + unsigned long len); >>>>> + >>>>> /* >>>>> * Clear the page's PageMlocked(). This can be useful in a situatio= n 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(un= signed 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; >>>>>=20 >>>>=20 >>>> 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? >>>=20 >>> Well, with the current implementation there are three limits an >>> administrator can use to control secretmem limits: mlock, memcg and >>> kernel parameter. >>>=20 >>> 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. >>>=20 >>> I didn't consider a dedicated cgroup, as it seems we already have enough= >>> existing knobs and a new one would be unnecessary. >>=20 >> 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 :) )? >=20 > Secretmem does not explicitly calls to mlock() but it does what mlock() > does and a bit more. Citing mlock(2): >=20 > 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. >=20 > So, based on that secretmem pages are not swappable, I think that > RLIMIT_MEMLOCK is appropriate here. >=20 The page explicitly lists mlock() system calls. E.g., we also don=E2=80=98t a= ccount for gigantic pages - which might be allocated from CMA and are not sw= appable. >> I mean, my concern is not earth shattering, this can be reworked later. A= s I >> said, it just feels wrong. >>=20 >> --=20 >> Thanks, >>=20 >> David / dhildenb >>=20 >=20 > --=20 > Sincerely yours, > Mike. >=20