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 A9E0743A80B; Fri, 11 Sep 2026 19:13:32 +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=1789154024; cv=none; b=brRl2bFTJGXkzUtKSGsxyYluCf+95sevxasDYxuWUu0KS936G5G1nGrQ4uPuSBjSReSjmy2+r+BggSUNJH+neQjmqQzcuAse4CcFHqnkSw+NQ9yLUtllGZK2Qj1/VOJVjncun8BzzDaxB7fsbhVwjsOOQeeG1j9sdCzK1jAfhTA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789154024; c=relaxed/simple; bh=jvizM2aN7IRIy6Qn/7yRhwj0YOKroV/6zbAOheS7Yl8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=V1IOj9rfIN28URxBHCFsqvHAAfUfmnoUmu/mH1FHKpc1vT5Ig7ll3pSte2BUYwpzVmHB6GjjJi6wPHYG0FhoT1Xu9DT5pdq7lcUOsvP3B0BiK1/avalamNdNvw51D24pgD+PEuFzuJ3nwAqvCwUTV1U2rh8S+AHOWbxYOoc5k0k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Pnylu3mz; 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="Pnylu3mz" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 361641F000FF; Fri, 11 Sep 2026 19:13:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789154010; bh=UUc6Gtsn7yXkmQKX9aijNaPvANqPVntk6MiQlVr6hUM=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=Pnylu3mzOr6v1ZBz0wjTh19bCz/9DAK2vb4NwfQuFbaPLsPuE/dNY6et4CV0XsHRe GYKfMyJ3lNi9W720j0ixURhcYU/SgZn9T3ABq0VBUyImLt+7Sk7oMSIMaRNzVZ20Ko 1zmfRHFaPAgn9EDzrEx0fBon2GcPxgBEBhyzJlOXHeLfE5WqGfQ7ECBlszVMwb3H6R 1lzYqveq7Cga1xrux17QswV4N8GydXPO6yMBM++y+j9pUj0+WpgC+rBhfdbhsxbyMo fTjr25Ft6G6sSnsiSAKoNte7LAoQXCepQs8pJH4f/UOFF1o48Vi3AHfjeqFt/hLrXl peowQiRKl+jng== Date: Fri, 11 Sep 2026 20:13:24 +0100 From: "Lorenzo Stoakes (ARM)" To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, liam@infradead.org, vbabka@kernel.org, david@redhat.com, willy@infradead.org, jannh@google.com, paulmck@kernel.org, pfalcato@suse.de, xueyuan.chen21@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH v3 5/7] proc/task_mmu: change proc_get_vma() to stop returning gate VMA at the end Message-ID: References: <20260910234737.1340642-1-surenb@google.com> <20260910234737.1340642-6-surenb@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Fri, Sep 11, 2026 at 12:11:55PM -0700, Suren Baghdasaryan wrote: > On Fri, Sep 11, 2026 at 12:03 PM Lorenzo Stoakes (ARM) wrote: > > > > On Fri, Sep 11, 2026 at 07:26:49PM +0100, Lorenzo Stoakes (ARM) wrote: > > > On Thu, Sep 10, 2026 at 04:47:35PM -0700, Suren Baghdasaryan wrote: > > > > proc_get_vma() returning gate VMA at the end is desirable for the its > > > > current m_start/m_next callers, as they need to report a gate VMA at the > > > > end of the address space. This behavior is very specific to these callers > > > > and makes proc_get_vma() hard to use for other purposes. > > > > > > > > Move this usage-specific behavior into the callers themselves so that > > > > proc_get_vma() returns either a valid VMA, an error or a NULL when no > > > > more VMAs are available. This makes it more generic, simpler and usable > > > > in the later patches. > > > > > > > > Signed-off-by: Suren Baghdasaryan > > > > > > Yes, very good change, thanks! > > > > > > Reviewed-by: Lorenzo Stoakes (ARM) > > > > > > > --- > > > > fs/proc/task_mmu.c | 23 ++++++++++++++++++----- > > > > 1 file changed, 18 insertions(+), 5 deletions(-) > > > > > > > > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > > > > index ecce7ce116cb..9a3c996c1d61 100644 > > > > --- a/fs/proc/task_mmu.c > > > > +++ b/fs/proc/task_mmu.c > > > > @@ -236,9 +236,6 @@ static struct vm_area_struct *proc_get_vma(struct seq_file *m, loff_t *ppos) > > > > * found the extended vma with the same vm_start. > > > > */ > > > > *ppos = vma->vm_end; > > > > - } else { > > > > - *ppos = SENTINEL_VMA_GATE; > > > > - vma = get_gate_vma(priv->lock_ctx.mm); > > > > > > Yeah this is just so confusing as-was. > > > > > > > } > > > > > > > > return vma; > > > > @@ -248,6 +245,7 @@ static void *m_start(struct seq_file *m, loff_t *ppos) > > > > { > > > > struct proc_maps_private *priv = m->private; > > > > struct proc_maps_locking_ctx *lock_ctx; > > > > + struct vm_area_struct *vma; > > > > loff_t last_addr = *ppos; > > > > struct mm_struct *mm; > > > > > > > > @@ -280,16 +278,31 @@ static void *m_start(struct seq_file *m, loff_t *ppos) > > > > if (last_addr == SENTINEL_VMA_GATE) > > > > return get_gate_vma(mm); > > > > > > > > - return proc_get_vma(m, ppos); > > > > + vma = proc_get_vma(m, ppos); > > > > + if (vma) > > > > + return vma; > > > > + > > > > + /* Return gate VMA at the end */ > > > > + *ppos = SENTINEL_VMA_GATE; > > > > + return get_gate_vma(mm); > > > > } > > > > > > > > static void *m_next(struct seq_file *m, void *v, loff_t *ppos) > > > > { > > > > + struct proc_maps_private *priv = m->private; > > > > + struct vm_area_struct *vma; > > > > + > > > > if (*ppos == SENTINEL_VMA_GATE) { > > > > *ppos = SENTINEL_VMA_END; > > > > return NULL; > > > > } > > > > - return proc_get_vma(m, ppos); > > > > + vma = proc_get_vma(m, ppos); > > > > + if (vma) > > > > + return vma; > > > > > > OK so I guess the logic is, iterate through every VMA, then once you run out, > > > report the gate VMA. Makes sense. > > > > Hmm one thing on this though - m_start() still has: > > > > if (last_addr == SENTINEL_VMA_GATE) > > return get_gate_vma(mm); > > > > As well as: > > > > vma = proc_get_vma(m, ppos); > > if (vma) > > return vma; > > > > /* Return gate VMA at the end */ > > *ppos = SENTINEL_VMA_GATE; > > return get_gate_vma(mm); > > > > Now at the end. > > > > Is this correct? Is it maybe duplicated now? > > Yeah, I noticed that too but I it's not duplication. The first check > handles the case when right after m_next() hit the end of the address > space and set *ppos = SENTINEL_VMA_GATE, we ran out of page space and > had to flush its content. Once that's done, m_start will be called and > last_addr will be set to SENTINEL_VMA_GATE. In that case we should > return get_gate_vma() and avoid calling proc_get_vma(). That's what > the first check for sentinel is doing. The second one handles the case > when m_start() itself readches the end of the address space and has to > return SENTINEL_VMA_GATE. > > It's possible this can be refactored a bit and made cleaner but I > would keep that as a separate change. Maybe just add a comment to the first one to explain when it'll trigger? That should suffice, cleanups can be separate yes. > > > > > > > > > > + > > > > + /* Return gate VMA at the end */ > > > > + *ppos = SENTINEL_VMA_GATE; > > > > + return get_gate_vma(priv->lock_ctx.mm); > > > > } > > > > > > > > static void m_stop(struct seq_file *m, void *v) > > > > -- > > > > 2.55.0.1007.g17ff1f9808-goog > > > > > > > > > > -- > > > Cheers, Lorenzo > > > > -- > > Cheers, Lorenzo -- Cheers, Lorenzo