From: Uladzislau Rezki <urezki@gmail.com>
To: Baoquan He <bhe@redhat.com>
Cc: Uladzislau Rezki <urezki@gmail.com>,
linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>,
Lorenzo Stoakes <lstoakes@gmail.com>,
Christoph Hellwig <hch@infradead.org>,
Matthew Wilcox <willy@infradead.org>,
"Liam R . Howlett" <Liam.Howlett@oracle.com>,
Dave Chinner <david@fromorbit.com>,
"Paul E . McKenney" <paulmck@kernel.org>,
Joel Fernandes <joel@joelfernandes.org>,
Oleksiy Avramchenko <oleksiy.avramchenko@sony.com>
Subject: Re: [PATCH v2 7/9] mm: vmalloc: Support multiple nodes in vread_iter
Date: Wed, 13 Sep 2023 17:42:52 +0200 [thread overview]
Message-ID: <ZQHYfO0GTco4qPEF@pc636> (raw)
In-Reply-To: <ZQBqyDxVuCphprk2@MiWiFi-R3L-srv>
On Tue, Sep 12, 2023 at 09:42:32PM +0800, Baoquan He wrote:
> On 09/11/23 at 08:16pm, Uladzislau Rezki wrote:
> > On Mon, Sep 11, 2023 at 11:58:13AM +0800, Baoquan He wrote:
> > > On 08/29/23 at 10:11am, Uladzislau Rezki (Sony) wrote:
> > > > Extend the vread_iter() to be able to perform a sequential
> > > > reading of VAs which are spread among multiple nodes. So a
> > > > data read over the /dev/kmem correctly reflects a vmalloc
> > > > memory layout.
> > > >
> > > > Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
> > > > ---
> > > > mm/vmalloc.c | 67 +++++++++++++++++++++++++++++++++++++++++-----------
> > > > 1 file changed, 53 insertions(+), 14 deletions(-)
> > > >
> > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > > > index 4fd4915c532d..968144c16237 100644
> > > > --- a/mm/vmalloc.c
> > > > +++ b/mm/vmalloc.c
> > > ......
> > > > @@ -4057,19 +4093,15 @@ long vread_iter(struct iov_iter *iter, const char *addr, size_t count)
> > > >
> > > > remains = count;
> > > >
> > > > - /* Hooked to node_0 so far. */
> > > > - vn = addr_to_node(0);
> > > > - spin_lock(&vn->busy.lock);
> > >
> > > This could change the vread behaviour a little bit. Before, once we take
> > > vmap_area_lock, the vread will read out the content of snapshot at the
> > > moment. Now, reading out in one node's tree won't disrupt other nodes'
> > > tree accessing. Not sure if this matters when people need access
> > > /proc/kcore, e.g dynamic debugging.
> > >
> > With one big tree you anyway drop the lock after one cycle of reading.
> > As far as i see, kcore.c's read granularity is a PAGE_SIZE.
>
> With my understanding, kcore reading on vmalloc does read page by page,
> it will continue after one page reading if the required size is bigger
> than one page. Please see aligned_vread_iter() code. During the complete
> process, vmap_area_lock is held before this patch.
>
> >
> > >
> > > And, the reading will be a little slower because each va finding need
> > > iterate all vmap_nodes[].
> > >
> > Right. It is a bit tough here, because we have multiple nodes which
> > represent zones(address space), i.e. there is an offset between them,
> > it means that, reading fully one tree, will not provide a sequential
> > reading.
>
> Understood. Suppose the kcore reading on vmalloc is not critical. If I
> get chance to test on a machine with 256 cpu, I will report here.
>
It would be great! Unfortunately i do not have an access to such big
systems. What i have is 64 CPUs max system. If you, by chance can test
on bigger systems or can provide a temporary ssh access that would be
awesome.
--
Uladzislau Rezki
next prev parent reply other threads:[~2023-09-13 15:42 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-29 8:11 [PATCH v2 0/9] Mitigate a vmap lock contention v2 Uladzislau Rezki (Sony)
2023-08-29 8:11 ` [PATCH v2 1/9] mm: vmalloc: Add va_alloc() helper Uladzislau Rezki (Sony)
2023-09-06 5:51 ` Baoquan He
2023-09-06 15:06 ` Uladzislau Rezki
2023-08-29 8:11 ` [PATCH v2 2/9] mm: vmalloc: Rename adjust_va_to_fit_type() function Uladzislau Rezki (Sony)
2023-09-06 5:51 ` Baoquan He
2023-09-06 16:27 ` Uladzislau Rezki
2023-08-29 8:11 ` [PATCH v2 3/9] mm: vmalloc: Move vmap_init_free_space() down in vmalloc.c Uladzislau Rezki (Sony)
2023-09-06 5:52 ` Baoquan He
2023-09-06 16:29 ` Uladzislau Rezki
2023-08-29 8:11 ` [PATCH v2 4/9] mm: vmalloc: Remove global vmap_area_root rb-tree Uladzislau Rezki (Sony)
2023-08-29 14:30 ` kernel test robot
2023-08-30 14:48 ` Uladzislau Rezki
2023-09-07 2:17 ` Baoquan He
2023-09-07 9:38 ` Baoquan He
2023-09-07 9:40 ` Uladzislau Rezki
2023-09-07 9:39 ` Uladzislau Rezki
2023-09-07 9:58 ` Baoquan He
2023-09-08 1:51 ` HAGIO KAZUHITO(萩尾 一仁)
2023-09-08 4:43 ` Baoquan He
2023-09-08 5:01 ` HAGIO KAZUHITO(萩尾 一仁)
2023-09-08 6:44 ` Baoquan He
2023-09-08 11:25 ` Uladzislau Rezki
2023-09-08 11:38 ` Baoquan He
2023-09-08 13:23 ` Uladzislau Rezki
2023-09-11 2:38 ` Baoquan He
2023-09-11 16:53 ` Uladzislau Rezki
2023-09-12 13:19 ` Baoquan He
2023-08-29 8:11 ` [PATCH v2 5/9] mm: vmalloc: Remove global purge_vmap_area_root rb-tree Uladzislau Rezki (Sony)
2023-09-11 2:57 ` Baoquan He
2023-09-11 17:00 ` Uladzislau Rezki
2023-08-29 8:11 ` [PATCH v2 6/9] mm: vmalloc: Offload free_vmap_area_lock lock Uladzislau Rezki (Sony)
2023-09-06 6:04 ` Baoquan He
2023-09-06 19:16 ` Uladzislau Rezki
2023-09-07 0:06 ` Baoquan He
2023-09-07 9:33 ` Uladzislau Rezki
2023-09-11 3:25 ` Baoquan He
2023-09-11 17:10 ` Uladzislau Rezki
2023-09-12 13:21 ` Baoquan He
2023-08-29 8:11 ` [PATCH v2 7/9] mm: vmalloc: Support multiple nodes in vread_iter Uladzislau Rezki (Sony)
2023-09-11 3:58 ` Baoquan He
2023-09-11 18:16 ` Uladzislau Rezki
2023-09-12 13:42 ` Baoquan He
2023-09-13 15:42 ` Uladzislau Rezki [this message]
2023-09-14 3:02 ` Baoquan He
2023-09-14 3:36 ` Baoquan He
2023-09-14 3:38 ` Baoquan He
2023-09-13 10:59 ` Baoquan He
2023-09-13 15:38 ` Uladzislau Rezki
2023-08-29 8:11 ` [PATCH v2 8/9] mm: vmalloc: Support multiple nodes in vmallocinfo Uladzislau Rezki (Sony)
2023-09-15 13:02 ` Baoquan He
2023-09-15 18:32 ` Uladzislau Rezki
2023-08-29 8:11 ` [PATCH v2 9/9] mm: vmalloc: Set nr_nodes/node_size based on CPU-cores Uladzislau Rezki (Sony)
2023-09-15 13:03 ` Baoquan He
2023-09-15 18:31 ` Uladzislau Rezki
2023-08-31 1:15 ` [PATCH v2 0/9] Mitigate a vmap lock contention v2 Baoquan He
2023-08-31 16:26 ` Uladzislau Rezki
2023-09-04 14:55 ` Uladzislau Rezki
2023-09-04 19:53 ` Andrew Morton
2023-09-05 6:53 ` Uladzislau Rezki
2023-09-06 20:04 ` Lorenzo Stoakes
2023-09-07 9:15 ` Uladzislau Rezki
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