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. Please correct me if i am wrong. > > 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. > > Otherwise, the patch itself looks good to me. > > Reviewed-by: Baoquan He <bhe@xxxxxxxxxx> > Applied. Thank you for looking at it! -- Uladzislau Rezki
