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@xxxxxxxxx> > > > > --- > > > > 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
