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b=bLp7gKfVv/9idt34PBmdyss+uSKw2MKefryQrQaKGYAWWA+NaBBePteRGwjhZTf5D 56Mjj1k7nqRj3m6j999DvmlcY2YW/yRGz34KW67UpK9ml1Ved+Fx+AVqNeFDjhdqn6 nTTWZJSgJ8ffEQuZn5w2yUciiDNPvcTqvhv1e4AiKwtqdEBWwbbv9t3lJTenYuLYfX NZD5uPEmEPBeTGslQ3YItaQ1YVezpSEj8Z9lpr3hhDhx6EsoaF5Zfvb/jqmWWr6jqv woj3Vwb/dYXbBhm8tVzjrcyuZzQSU2YzUlKBrzg7EL0Iobu+0AVyZw5hSBXARpzIyc yt+zhN82B1EeA== Message-ID: Date: Wed, 10 Jun 2026 17:01:57 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/2] fs/proc/task_mmu: read proc/pid/smaps_rollup under per-vma lock To: Suren Baghdasaryan , Lorenzo Stoakes Cc: akpm@linux-foundation.org, liam@infradead.org, vbabka@kernel.org, willy@infradead.org, jannh@google.com, paulmck@kernel.org, pfalcato@suse.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Dave Hansen References: <20260606015729.1837935-1-surenb@google.com> <20260606015729.1837935-2-surenb@google.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 9DD61100015 X-Rspam-User: X-Stat-Signature: pkh9mw4cisghgx7u7omdb3hjos873zt5 X-Rspamd-Server: rspam08 X-HE-Tag: 1781103723-243604 X-HE-Meta: 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 wdGhwwlc MiszqZOOVRumPdHjsrTAnxeITTyASiqzQf+GwmvpEi7CFV2ev8pkkt/P11ae6IJ9KS/R2N768tPecFOzo2eNxeZANCr+3OdHAxvwbIoXHESwy9W1UY3MU0nQNn9512yjh90BYY1z76rW+b0l8YPqOOmQnLfeD3FU9WycIEQR5aTELx12t4KYCoQJKOCJ+9/c0NzdFN/yPennpge/t14r/x2vrEV07vdONJVTqBmTS6sPtQkpk0NHzd/e5TeTIJSOSY531wSmNQzdMFrkgrgAA5shVtwoBs4M2Av8eW858XdMyB92kCrs/YrECvi5u3JWIkY3mW2mb6kFUpqw65LlW9Jp/RTIW2ZYQoeT8DiCGkTfGNUQAU3W7RKgtyM03RTGycU8SlEKGc71VSMIpkJ47tgsyxcVQlLVvW/9H Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/10/26 16:56, Suren Baghdasaryan wrote: > On Wed, Jun 10, 2026 at 12:05 AM Lorenzo Stoakes wrote: >> >> On Tue, Jun 09, 2026 at 10:11:03AM -0700, Suren Baghdasaryan wrote: >>> >>> Ack. >>> >>> >>> Ack. >>> >>> >>> Sadly, for now we do (see my later comment). >>> >>> >>> It looked nicer I think :) >> >> Yeah tbh I think you're right >> >>> >>> >>> Ack. >>> >>> >>> We need it to avoid resetting vma_start, which is being reported even >>> when no normal VMAs are present. >> >> Well previously smap_gather_stats() would just be a no-op for a gate VMA, as it >> has: >> >> if (vma == get_gate_vma(priv->lock_ctx.mm)) >> return; >> >> Not sure if you'd have VMAs past that (is that even possible?) but in that case >> we would have set vma_start previously. > > I should explain this case in more detail. proc_get_vma() returns a > gate VMA once it finds no more VMAs. So, in this case if VMA tree is > empty, the first call to proc_get_vma() will return gate VMA. Now, the > original code was using vma_next() and would return NULL when the VMA > tree is empty and in that case it would bail out early here: > https://elixir.bootlin.com/linux/v7.1-rc7/source/fs/proc/task_mmu.c#L1423. > I need to use proc_get_vma() instead of vma_next() because it works > under RCU. So, the new code matches the previous behavior, but the > condition is different. I'll see if I can resolve this in a nicer way > but that's the gist of it. I guess some well-named helper that encapsulates the check would already help. But maybe the whole logic can be overhauled. -- Cheers, David