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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 10.11.54.1 X-Rspamd-Queue-Id: 767A0140006 X-Rspam-User: X-Stat-Signature: w6t8qs4tyzq31sa6sp81km19e3dkt494 X-Rspamd-Server: rspam01 X-HE-Tag: 1694662716-180109 X-HE-Meta: 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 zQQC5Q6V xTbZ5GiENpSo7tKphQI6LbDqrTg1jy1Ir+a/dnV4bx1LsIlSVt35z+kWWSZ2Eb4cMrcJiLGX3/8j0dBprP8vsVykR6g46K2Gi7sAHpkSb6kIW5ZgSZsKxpZtiqkFet1QJ+YUAB8TzNu0/PbNihq1eBsHG4cQm8XdmeMXZKmgL96AAMSJ4dTajbEdD/x58HXPMXdDqr8nbWqjgVNr1o52/C40G1JF7uhxDlEW4gWtFG5OM2p5X5MrIB0d6CWrZvpXI4st6qrPFb9r6uENJABaAt+LR+A== 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 09/14/23 at 11:36am, Baoquan He wrote: > 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. > > 10.16.216.205 > user:root > password:redhat > > This is a testing server in our lab, we apply for usage each time and it > will reinstall OS, root user should be OK. I will take it for two days. Oops, I sent it out publicly. > > If accessing is not available, I can do some testing if you want me to > run some commands. >