search for: page_ref_dec

...ers (so offlining code can correctly subtract > + * them again). > + */ > + pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) + > + sb_id * vm->subblock_size); > + adjust_managed_page_count(pfn_to_page(pfn), nr_pages); > + for (i = 0; i < nr_pages; i++) > + page_ref_dec(pfn_to_page(pfn + i)); Is there ever situation this might be a different than 1->0 transition? -- Michal Hocko SUSE Labs

...ers (so offlining code can correctly subtract > + * them again). > + */ > + pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) + > + sb_id * vm->subblock_size); > + adjust_managed_page_count(pfn_to_page(pfn), nr_pages); > + for (i = 0; i < nr_pages; i++) > + page_ref_dec(pfn_to_page(pfn + i)); Is there ever situation this might be a different than 1->0 transition? -- Michal Hocko SUSE Labs

...* them again). > >> + */ > >> + pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) + > >> + sb_id * vm->subblock_size); > >> + adjust_managed_page_count(pfn_to_page(pfn), nr_pages); > >> + for (i = 0; i < nr_pages; i++) > >> + page_ref_dec(pfn_to_page(pfn + i)); > > > > Is there ever situation this might be a different than 1->0 transition? > > Only if some other code would be taking a reference. At least not from > virtio-mem perspective. OK, so that is essentially an error condition. I think it shouldn...

...e to the allocator (via put_page). You can also set > the reference count to 0 explicitly. The driver is in control of the > page, right? And that is the whole point I wanted to make. There is an This is what virtio-mem does whenever it allocates a range using alloc_contig_range(). It uses page_ref_dec() instead of put_page() /* * Set a range of pages PG_offline and drop the reference. The dropped * reference (0) and the flag allows isolation code to isolate thisrange * and offline code to offline it. */ static void virtio_mem_set_fake_offline(unsigned long pfn,...

On Fri 18-10-19 10:50:24, David Hildenbrand wrote: > On 18.10.19 10:15, Michal Hocko wrote: > > On Wed 16-10-19 16:14:52, David Hildenbrand wrote: > > > On 16.10.19 16:03, Michal Hocko wrote: > > [...] > > > > But why cannot you keep the reference count at 1 (do get_page when > > > > offlining the page)? In other words as long as the driver knows the

On Fri 18-10-19 10:50:24, David Hildenbrand wrote: > On 18.10.19 10:15, Michal Hocko wrote: > > On Wed 16-10-19 16:14:52, David Hildenbrand wrote: > > > On 16.10.19 16:03, Michal Hocko wrote: > > [...] > > > > But why cannot you keep the reference count at 1 (do get_page when > > > > offlining the page)? In other words as long as the driver knows the

...arely used on most systems) doesn't sound nice to me. > > This is the whole point which made me think about the whole reference > > count approach in the first place. > > Again, the race I think that is possible > > somebody: get_page_unless_zero(page) > virtio_mem: page_ref_dec(pfn_to_page(pfn) > somebody: put_page() -> straight to the buddy Who is that somebody? I thought that it is only the owner/driver to have a control over the page. Also the above is not possible as long as the owner/driver keeps a reference to the PageOffline page throughout the time it is ma...

...arely used on most systems) doesn't sound nice to me. > > This is the whole point which made me think about the whole reference > > count approach in the first place. > > Again, the race I think that is possible > > somebody: get_page_unless_zero(page) > virtio_mem: page_ref_dec(pfn_to_page(pfn) > somebody: put_page() -> straight to the buddy Who is that somebody? I thought that it is only the owner/driver to have a control over the page. Also the above is not possible as long as the owner/driver keeps a reference to the PageOffline page throughout the time it is ma...

...orrectly subtract >> + * them again). >> + */ >> + pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) + >> + sb_id * vm->subblock_size); >> + adjust_managed_page_count(pfn_to_page(pfn), nr_pages); >> + for (i = 0; i < nr_pages; i++) >> + page_ref_dec(pfn_to_page(pfn + i)); > > Is there ever situation this might be a different than 1->0 transition? Only if some other code would be taking a reference. At least not from virtio-mem perspective. -- Thanks, David / dhildenb

...ges to the managed + * page counters (so offlining code can correctly subtract + * them again). + */ + pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) + + sb_id * vm->subblock_size); + adjust_managed_page_count(pfn_to_page(pfn), nr_pages); + for (i = 0; i < nr_pages; i++) + page_ref_dec(pfn_to_page(pfn + i)); + } +} + +static void virtio_mem_notify_cancel_offline(struct virtio_mem *vm, + unsigned long mb_id) +{ + const unsigned long nr_pages = PFN_DOWN(vm->subblock_size); + unsigned long pfn; + int sb_id, i; + + for (sb_id = 0; sb_id < vm->nb_sb_per_mb; sb_id++)...

...ms) doesn't sound nice to me. >>> This is the whole point which made me think about the whole reference >>> count approach in the first place. >> >> Again, the race I think that is possible >> >> somebody: get_page_unless_zero(page) >> virtio_mem: page_ref_dec(pfn_to_page(pfn) >> somebody: put_page() -> straight to the buddy > > Who is that somebody? I thought that it is only the owner/driver to have > a control over the page. Also the above is not possible as long as the > owner/driver keeps a reference to the PageOffline page thro...

...gt; >>> This is the whole point which made me think about the whole reference > >>> count approach in the first place. > >> > >> Again, the race I think that is possible > >> > >> somebody: get_page_unless_zero(page) > >> virtio_mem: page_ref_dec(pfn_to_page(pfn) > >> somebody: put_page() -> straight to the buddy > > > > Who is that somebody? I thought that it is only the owner/driver to have > > a control over the page. Also the above is not possible as long as the > > owner/driver keeps a reference to...

...gt; >>> This is the whole point which made me think about the whole reference > >>> count approach in the first place. > >> > >> Again, the race I think that is possible > >> > >> somebody: get_page_unless_zero(page) > >> virtio_mem: page_ref_dec(pfn_to_page(pfn) > >> somebody: put_page() -> straight to the buddy > > > > Who is that somebody? I thought that it is only the owner/driver to have > > a control over the page. Also the above is not possible as long as the > > owner/driver keeps a reference to...

This series is based on latest linux-next. The patches are located at: https://github.com/davidhildenbrand/linux.git virtio-mem-v1 The basic idea of virtio-mem is to provide a flexible, cross-architecture memory hot(un)plug solution that avoids many limitations imposed by existing technologies, architectures, and interfaces. More details can be found below and in linked material. It's

This series is based on latest linux-next. The patches are located at: https://github.com/davidhildenbrand/linux.git virtio-mem-v1 The basic idea of virtio-mem is to provide a flexible, cross-architecture memory hot(un)plug solution that avoids many limitations imposed by existing technologies, architectures, and interfaces. More details can be found below and in linked material. It's

This series is based on latest linux-next. The patches are located at: https://github.com/davidhildenbrand/linux.git virtio-mem-rfc-v4 The basic idea of virtio-mem is to provide a flexible, cross-architecture memory hot(un)plug solution that avoids many limitations imposed by existing technologies, architectures, and interfaces. More details can be found below and in linked material. This

This series is based on latest linux-next. The patches are located at: https://github.com/davidhildenbrand/linux.git virtio-mem-rfc-v4 The basic idea of virtio-mem is to provide a flexible, cross-architecture memory hot(un)plug solution that avoids many limitations imposed by existing technologies, architectures, and interfaces. More details can be found below and in linked material. This

Long time no RFC! I finally had time to get the next version of the Linux driver side of virtio-mem into shape, incorporating ideas and feedback from previous discussions. This RFC is based on the series currently on the mm list: - [PATCH 0/3] Remove __online_page_set_limits() - [PATCH v1 0/3] mm/memory_hotplug: Export generic_online_page() - [PATCH v4 0/8] mm/memory_hotplug: Shrink zones before