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[90.235.20.237]) by smtp.gmail.com with ESMTPSA id z7-20020a2e9b87000000b002b9fe77d00dsm2455243lji.93.2023.09.13.08.42.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 13 Sep 2023 08:42:54 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Wed, 13 Sep 2023 17:42:52 +0200 To: Baoquan He Cc: Uladzislau Rezki , linux-mm@kvack.org, Andrew Morton , LKML , Lorenzo Stoakes , Christoph Hellwig , Matthew Wilcox , "Liam R . 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-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: EFDA3180024 X-Stat-Signature: a5dru77dx8g4fg7nn4d8ck3xq8kn4wi9 X-HE-Tag: 1694619776-325321 X-HE-Meta: U2FsdGVkX1/lW30O3pnN3CaQKd4Vzim52FKtgvFb4iPcTvGULSDIL/33c4d7ttPGqXROSt75U3jBi8vLqJMH5uTuKGKDePfk21hk8gaRs8lXITmTrv5Jfq8b5tdY96omxMrwVo2CnMBfGU7NqckFycUHqJKVGkd1Hu04FpVOXkrDgW/ULiEkev6l6rBZxBhkiZv83vFch9ApNbA2mLnxxCQUjR3s6YwP3LxHO9jkSyKjx650MXAB4rza88w/lniXlVyYfAnqCLVEXUNJ7+hqxr7uS0AAVl5VvtxiUQBbDTpnGe7+rpYgSpzQQ4Ph4D78G7lfOhf7aUxRP5R7RhlSFCHw/VDYHT2olJg3tQ9AJXCCGq9LNoZjE6vSP2S/3r3CkkIvMDh3G4iOMiqEVWLlt/rkbGgnd+MJLGoNUjnQasTaum1JIZVtfh7YeJmIvoS2wk26uZrLXXldLMvDuxocMzrM19nNbfVx9SyxastAVg8U526hsiuDAaHe5pq7JkkYWWC5JecNS6FKmtkYNPX5Fgrnzi8CiHjGUy/eIXW/Yad1IZSjFhvV4abTdoETjA4GJcQgBr/LJAJ5YEzgz4eT0TRaiSH6YOgpeDfYRSX+O+yyzpBur4I3H0PtWAsMAbwzeyQNqBw35PohZSf/fb8MMWVYv1pej2gKATaJINxd4wtUhKGZrhpyZydvDf6lqmm0tLmlVI8iR8z5wCjoRNb+odpuxdjAfxxcMFGgKB9lWzrEjk3lJz6gZlS/3meh9ZZ5G9gEC731vBqD0tCAtVILUDSBvz5i/yb91+EnqMCgPytye3npQS/Vz16mF3u/5ryjvtUxQks4zDPNEEJ950T0ouf6j/uXetcHZ/UoI11ezQCF+nMWNDoTpFIsqrYcqCKPnsF/2eyH6XoKy4z5q5AEbzrO9PNP4luPkmgAIcOYueP65xUWI2zltKR2/m3OnXbozdkIdfeICwuofAxnxzj /cj8C2vd 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 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 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. -- Uladzislau Rezki