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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 10.11.54.2 X-Rspamd-Queue-Id: 58CE414000E X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: 6f38w7uwqxki9gxzpx4tkrafxum176tb X-HE-Tag: 1694662577-779736 X-HE-Meta: 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 wE8Dshx5 vR/zTXolRVOjVI+9yaL9LPdR0WsrBuJRIl+M9SXHfjYZghu4VGOdnuBC4t7wHBHQkKn0wvDouVPdVm3avoMIJFpaZLGho/hlN6JdzTiptTXBuW1wKoU0LABmiKaZEyrkRSA1XHgB78NqKYhhVCHIE4srIrro8t4Htc+SPIrE/PDxuNKitjKpGrFXlBe13mjVykYfGX2aEfAQ5XWDsxnafwnPRKZHA/Bvg3ypPF6v8n6UeRbJsr+w6E9/PZ5IgC8Dc+0nwiPRZ4eptn9ZxL4ChkowKBg== 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. 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. If accessing is not available, I can do some testing if you want me to run some commands.