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[2003:cb:c725:8700:77c7:bde:9446:8d34]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-42f86b44374sm87917245e9.30.2024.10.07.03.24.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 07 Oct 2024 03:24:57 -0700 (PDT) Message-ID: <04c4314e-7958-47bd-8281-23c3e35fc10e@redhat.com> Date: Mon, 7 Oct 2024 12:24:56 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v3 06/10] mm/mshare: Add vm flag for shared PTEs To: James Houghton , Anthony Yznaga Cc: akpm@linux-foundation.org, willy@infradead.org, markhemm@googlemail.com, viro@zeniv.linux.org.uk, khalid@kernel.org, andreyknvl@gmail.com, dave.hansen@intel.com, luto@kernel.org, brauner@kernel.org, arnd@arndb.de, ebiederm@xmission.com, catalin.marinas@arm.com, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mhiramat@kernel.org, rostedt@goodmis.org, vasily.averin@linux.dev, xhao@linux.alibaba.com, pcc@google.com, neilb@suse.de, maz@kernel.org References: <20240903232241.43995-1-anthony.yznaga@oracle.com> <20240903232241.43995-7-anthony.yznaga@oracle.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 3AED1180009 X-Stat-Signature: p8nchjbp77xywwt7oe4inkwt4hic66wi X-Rspam-User: X-HE-Tag: 1728296701-293545 X-HE-Meta: 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 lr5hYM/W 3SP13//wkt56G8r5BszC+LULGkHZE3qzP6ZD4AhgNwjCoL+uksY6iTT0quaaUFU9SNv42VYsMf1/c+hDfDztawlef5kRrSF7aXqo8zX26F9Uwe7YJevpsN1DoxXNjPwyIvXLNIUUVW3cYpSU6MsVIRPodDLnlqsAPi1Ry3cWpFs+nMQXsSd4JfdT5EUM4rAoW3wZCM4w2xwn6o9081m/3hKQzEJwxHgVULMVZWuV6RQenU45S6Bqom3tPmhJDJMVCz2wQagQUst75AwdIEh7CrrFAhAvQo+gA2rXoIqagUR3LcU2lYiqzzfPJOsLjWKoOh4aAqyv15/JqNQpcgiszeb9bijWYejze69cLGlEQErjcuxOmQLTS9MvfbPjFiVvsJUKWKnG6jvQy4VArnHj/E3fJE/yQlAECP9jCTl7CwdBDuatztSjTKRGDbrFqC2xH+DpkZaxmUP4zMa8vqD9T2207u0ikRPKK1yN2vVmsfWfx0X8+8B7fXol8QXrrMWVuREWhZDLw3N2D+oHLoBeU99BoDA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 04.09.24 01:40, James Houghton wrote: > On Tue, Sep 3, 2024 at 4:23 PM Anthony Yznaga wrote: >> >> From: Khalid Aziz >> >> Add a bit to vm_flags to indicate a vma shares PTEs with others. Add >> a function to determine if a vma shares PTEs by checking this flag. >> This is to be used to find the shared page table entries on page fault >> for vmas sharing PTEs. >> >> Signed-off-by: Khalid Aziz >> Signed-off-by: Matthew Wilcox (Oracle) >> Signed-off-by: Anthony Yznaga >> --- >> include/linux/mm.h | 7 +++++++ >> include/trace/events/mmflags.h | 3 +++ >> mm/internal.h | 5 +++++ >> 3 files changed, 15 insertions(+) >> >> diff --git a/include/linux/mm.h b/include/linux/mm.h >> index 6549d0979b28..3aa0b3322284 100644 >> --- a/include/linux/mm.h >> +++ b/include/linux/mm.h >> @@ -413,6 +413,13 @@ extern unsigned int kobjsize(const void *objp); >> #define VM_DROPPABLE VM_NONE >> #endif >> >> +#ifdef CONFIG_64BIT >> +#define VM_SHARED_PT_BIT 41 >> +#define VM_SHARED_PT BIT(VM_SHARED_PT_BIT) >> +#else >> +#define VM_SHARED_PT VM_NONE >> +#endif >> + >> #ifdef CONFIG_64BIT >> /* VM is sealed, in vm_flags */ >> #define VM_SEALED _BITUL(63) >> diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h >> index b63d211bd141..e1ae1e60d086 100644 >> --- a/include/trace/events/mmflags.h >> +++ b/include/trace/events/mmflags.h >> @@ -167,8 +167,10 @@ IF_HAVE_PG_ARCH_X(arch_3) >> >> #ifdef CONFIG_64BIT >> # define IF_HAVE_VM_DROPPABLE(flag, name) {flag, name}, >> +# define IF_HAVE_VM_SHARED_PT(flag, name) {flag, name}, >> #else >> # define IF_HAVE_VM_DROPPABLE(flag, name) >> +# define IF_HAVE_VM_SHARED_PT(flag, name) >> #endif >> >> #define __def_vmaflag_names \ >> @@ -204,6 +206,7 @@ IF_HAVE_VM_SOFTDIRTY(VM_SOFTDIRTY, "softdirty" ) \ >> {VM_HUGEPAGE, "hugepage" }, \ >> {VM_NOHUGEPAGE, "nohugepage" }, \ >> IF_HAVE_VM_DROPPABLE(VM_DROPPABLE, "droppable" ) \ >> +IF_HAVE_VM_SHARED_PT(VM_SHARED_PT, "sharedpt" ) \ >> {VM_MERGEABLE, "mergeable" } \ >> >> #define show_vma_flags(flags) \ >> diff --git a/mm/internal.h b/mm/internal.h >> index b4d86436565b..8005d5956b6e 100644 >> --- a/mm/internal.h >> +++ b/mm/internal.h >> @@ -1578,4 +1578,9 @@ void unlink_file_vma_batch_init(struct unlink_vma_file_batch *); >> void unlink_file_vma_batch_add(struct unlink_vma_file_batch *, struct vm_area_struct *); >> void unlink_file_vma_batch_final(struct unlink_vma_file_batch *); >> > > Hi Anthony, > > I'm really excited to see this series on the mailing list again! :) I > won't have time to review this series in too much detail, but I hope > something like it gets merged eventually. > >> +static inline bool vma_is_shared(const struct vm_area_struct *vma) >> +{ >> + return VM_SHARED_PT && (vma->vm_flags & VM_SHARED_PT); >> +} > > Tiny comment - I find vma_is_shared() to be a bit of a confusing name, > especially given how vma_is_shared_maywrite() is defined. (Sorry if > this has already been discussed before.) > > How about vma_is_shared_pt()? vma_is_mshare() ? ;) The whole "shared PT / shared PTE" is a bit misleading IMHO and a bit too dominant in the series. Yes, we're sharing PTEs/page tables, but the main point is that a single mshare VMA might cover multiple different VMAs (in a different process). I would describe mshare VMAs as being something that shares page tables with another MM, BUT, also that the VMA is a container and what exactly the *actual* VMAs in there are (including holes), only the owner knows. E.g., is_vm_hugetlb_page() might be *false* for an mshare VMA, but there might be hugetlb folios mapped into the page tables, described by a is_vm_hugetlb_page() VMA in the owner MM. So again, it's not just "sharing page tables". -- Cheers, David / dhildenb