From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1A68841B360; Wed, 10 Jun 2026 15:02:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781103724; cv=none; b=rIU6NMuVCjTzmtwnJgMH+i87jg2tt75ldqTFOq/FUEvhO6M6GyuObcGJA/UzzQACguCMnep6lqW+kvMaoWcdOqPm7bfj3mL413RWuuRA/7FWDiAmOH+cXcUVv+wihPCWXQX0SNbe9UUv7N7hntBMCEkkTMwAWbPQ9r7hix93tIo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781103724; c=relaxed/simple; bh=2NAR6Hhxj8b0YM51APAGnZ8eJEN/AQwxZsbmb71mL/8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Z0oe0iHqcGZ0HaU5O2L4Ee44W6tnbvg2kdPw9FAzOboh5LLbdc2ciNHgbEMczF7aWTvlXZnPTw1FwV58LUV4PFdD3JT1Z84YzF1LiqyHtLPHS1GMmBPHy7o9E3vaiNzeddVoZRyJn3POPzWK774FG9yBdUxoMb+jPwBamPLSMXQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bLp7gKfV; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="bLp7gKfV" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 93DBD1F00893; Wed, 10 Jun 2026 15:01:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781103722; bh=vBNtytDEfxL/pz+YWvvBjkIv0STW5xtFZ5ArtldVzng=; h=Date:Subject:To:Cc:References:From:In-Reply-To; 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 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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