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) <[email protected]>
> > > ---
> > > 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.
You are right, kcore.c's reading granularity is truly PAGE_SIZE.
I don't know procfs well, still need to study the code. Then it doesn't
matter much with the multiple nodes in vread_iter(). Sorry for the noise.
static ssize_t read_kcore_iter(struct kiocb *iocb, struct iov_iter *iter)
{
......
start = kc_offset_to_vaddr(*fpos - data_offset);
if ((tsz = (PAGE_SIZE - (start & ~PAGE_MASK))) > buflen)
tsz = buflen;
m = NULL;
while (buflen) {
}
...
}
On Wed, Sep 13, 2023 at 06:59:42PM +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) <[email protected]>
> > > > ---
> > > > 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.
>
> You are right, kcore.c's reading granularity is truly PAGE_SIZE.
> I don't know procfs well, still need to study the code. Then it doesn't
> matter much with the multiple nodes in vread_iter(). Sorry for the noise.
>
> static ssize_t read_kcore_iter(struct kiocb *iocb, struct iov_iter *iter)
> {
> ......
> start = kc_offset_to_vaddr(*fpos - data_offset);
> if ((tsz = (PAGE_SIZE - (start & ~PAGE_MASK))) > buflen)
> tsz = buflen;
>
> m = NULL;
> while (buflen) {
> }
> ...
> }
>
Good. Then we are on the same page :)
Thank you!
--
Uladzislau Rezki