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Howlett" , Dave Chinner , "Paul E . McKenney" , Joel Fernandes , Oleksiy Avramchenko Subject: Re: [PATCH v2 7/9] mm: vmalloc: Support multiple nodes in vread_iter Message-ID: References: <20230829081142.3619-1-urezki@gmail.com> <20230829081142.3619-8-urezki@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6 X-Rspamd-Queue-Id: 20E8040008 X-Rspam-User: X-Stat-Signature: i797un4ss6f6rdywqzc9jugettnd3cr7 X-Rspamd-Server: rspam01 X-HE-Tag: 1694660582-691330 X-HE-Meta: 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 cC5yx9k0 iUaQgqKl4ctVZ8VB+rIR8tJfCkxZZZ71w5RdCZ5kWAC+S6PrqopcxtFDdZAbYKba7t9eXoQdq82cb1MRu/0VLnbnNXEnuCBFpz+RXDWPgEtdisF17alZGREeCCrfkPUHdkjlj4J1so6FZZ0CNTSWLwwxQ+VorBMRbgtqAYYFhjgdd12oSq7OheiuzP7l4HwkypJvoWsSssvS/SFvly+S2YoJl9tfEyBi0PVEh5bLm5nArHBvsLxfcDTM7RendKJm6Nt0k7dXicyJcCAUe6KJ3TjfTPA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 09/13/23 at 05:42pm, Uladzislau Rezki wrote: > 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) > > > > > --- > > > > > 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. I got one with 288 cpus, have sent you ip address in private mail.