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b=JMsyThF+eFING3jywDW0rCma9gBDFSSk9za7CH91vogQleXQjw0OVhjzTcvJtUlpq Ro01gdMnSouNoCkjH/sI1zR5/UG8e/bodteawGjp5FGv2zR7905Po83AAEZE72tS9A z2EKdi0NWqdrj+9MIDgM9rPgD1MisZ0DQKzWYyBrSb0EtChz3sfBlEo8uwZCKiiz7Q kbNRycbizvQc4D/+xWVrcrpLXolXYmuooi/e7vvg8CxL0+gvtrw8I0b2K6LIBU6aXw IZy+IN1zGvMgMNP+UJgc1sv4BED3yUlNrPNUdom3Qyr/mm/5kr9QBo/dBu89An5or6 wIra8LV56l1og== Date: Fri, 11 Sep 2026 20:26:52 +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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 2BDC440004 X-Stat-Signature: m5o7k13c39ou9kgqy97dawh4qo143ftp X-HE-Tag: 1789154819-655472 X-HE-Meta: U2FsdGVkX1//gzqwxbZ0BVta6J8HDIX9NZlVrhpOWdpca8ECoqK7olihmIjo9uBQto+R9EVn27DRX05kYaTBFt+Wkwuvy51WUhxwjSVZljVl9sf77naYPaAeh9hDWdHzZOjs8bZZEIC6VuavvEgkwdxsj9cs6dgudF+dri5Lv72nuWiT0y8EEWvXhShsUh0sy2wkfU9T5Koo91C4O+jdt7lw6iHwrsJBmjVKnGnHwHWYEpJD5vLJ88XUQ1d5u5M0cFXXIQV4KCVa6PXgKIq3aQf+HQ2PpIcDzC4wqitcnOB7VBpsLZOW4IRl+k6MeQLNAUN//81m0UBH2xP4OUcEWyy54GFaydzKvBV4wPRXO5KFnv7M/SD516Pa8YGT+6OkunQVVO0XUsYH03pVsGzqiRRxPuhhLqfSoexy9tiMCbS5L+FEUWfhJuQfFjiirbwXxPx8syPXrXs1xxcu+KYnhIBDzq6xSxUtZMQtHdhXyrxt/7IgYuMOD/lteAx/iH1cX+K+LwMB/nLHGntbeCybLRwIzpdCXBPLHf/E68VKfw/QImaO3G64oAeP4Hg39M0YhsKHiJ9KemSm9v7SPauEowMQzzUBIEh9eOrjpGvdpujKmaZV327oYeSvKD0p3qRAG9olhxiU8mrNDqrghrmJyQTi8z8htirrVDVnG/fjzlO5BievNUY+f7TRC4DXAKC8VByMrPC9Z1dMg1q0h0jw3Agro+FRB/XJYpgcHJWeZ/DZluu71n5MSosO80h5326beF7qmuSi6LmXqPg2SyOvb9aX4QGzhBeUCloN1ZJoBWWzE7OC4qC55rmIQeRZw0jnilsA3QYAuyp9kzI0cIv/YX83yToYauybEg/X29fs5Snv3GbmmsGe3AuUy0QcSycNURkaf1Dohv7jlt1JZcRaal2I0gTYsl6EFMcMxu4RdQvApQmyojtM5dEpyCpF6f0Ji6N8+vSheComtqXjrpU a3EncbiZ vzvdytdjm2D7xj9hex/sDYT9mocQ3PxTkIvym4lLZWilTV7hTYpLKWrsmdWFe82SzY6jjwHu1MUJVCTMXUsS0S0lM5oBIEoieuAcOehz0qhAvKvWoxB6m2jL7oa33Drz4HkwQidfk3+qTcEDPdom+VbTUXABft5CLG2SEHeJnfSTj5JA828JUp+92slQSOr9tvRS5MCbzVTV1KyPaSFP9l0MX0Ua0iCxewnXXzdVlT9H45dUmJqXbKgYp7WuShQ8AVjys3x3ZgAcP+FmlslM1Q81R69DPhdJsSN9jEPKqfw6j9Mj/0jE4ADXLILqy7tH/U50REY2s+bw2S/owgWY4jNsR7gezDrJlZElhcv3+daZiIn3GSwICjyUvpPQT52e9LLCvFisCjVk6qaI7JrSnHrBDns8C+Iocn0sZUPrqKsVf0uHSGUYkOAN2xG2BuAX5vHX4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Sep 11, 2026 at 12:18:41PM -0700, Suren Baghdasaryan wrote: > On Fri, Sep 11, 2026 at 12:13 PM Lorenzo Stoakes (ARM) wrote: > > > > 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. > > Will do. Appreciate the reviews! > > I'll post the update today because there is some urgency to backport > these patches and I want to have a public link when backporting but I > don't expect anyone to burn the midnight oil to review the final > version. Have a nice weekend! Well you have tags on most things from me now so it'll only be one patch I think? That'll be missing mine anyway. > > > > > > > > > > > > > > > > > > > > > + > > > > > > + /* 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 -- Cheers, Lorenzo