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.
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.
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) <[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.
>
> 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
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) <[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.
> >
> > 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.
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) <[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.
> >
> > 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.
I got one with 288 cpus, have sent you ip address in private mail.