On Mon, Jun 19, 2023 at 03:53:40PM +0800, mawupeng wrote: > > > On 2023/6/19 15:41, David Hildenbrand wrote: > > On 19.06.23 09:22, mawupeng wrote: > >> > >> > >> On 2023/6/19 15:16, Greg KH wrote: > >>> On Mon, Jun 19, 2023 at 02:51:21PM +0800, Wupeng Ma wrote: > >>>> From: David Hildenbrand <david@xxxxxxxxxx> > >>>> > >>>> commit 8dc4bb58a146655eb057247d7c9d19e73928715b upstream. > >>>> > >>>> virtio-mem soon wants to use offline_and_remove_memory() memory that > >>>> exceeds a single Linux memory block (memory_block_size_bytes()). Let's > >>>> remove that restriction. > >>>> > >>>> Let's remember the old state and try to restore that if anything goes > >>>> wrong. While re-onlining can, in general, fail, it's highly unlikely to > >>>> happen (usually only when a notifier fails to allocate memory, and these > >>>> are rather rare). > >>>> > >>>> This will be used by virtio-mem to offline+remove memory ranges that are > >>>> bigger than a single memory block - for example, with a device block > >>>> size of 1 GiB (e.g., gigantic pages in the hypervisor) and a Linux memory > >>>> block size of 128MB. > >>>> > >>>> While we could compress the state into 2 bit, using 8 bit is much > >>>> easier. > >>>> > >>>> This handling is similar, but different to acpi_scan_try_to_offline(): > >>>> > >>>> a) We don't try to offline twice. I am not sure if this CONFIG_MEMCG > >>>> optimization is still relevant - it should only apply to ZONE_NORMAL > >>>> (where we have no guarantees). If relevant, we can always add it. > >>>> > >>>> b) acpi_scan_try_to_offline() simply onlines all memory in case > >>>> something goes wrong. It doesn't restore previous online type. Let's do > >>>> that, so we won't overwrite what e.g., user space configured. > >>>> > >>>> Reviewed-by: Wei Yang <richard.weiyang@xxxxxxxxxxxxxxxxx> > >>>> Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx> > >>>> Cc: Jason Wang <jasowang@xxxxxxxxxx> > >>>> Cc: Pankaj Gupta <pankaj.gupta.linux@xxxxxxxxx> > >>>> Cc: Michal Hocko <mhocko@xxxxxxxxxx> > >>>> Cc: Oscar Salvador <osalvador@xxxxxxx> > >>>> Cc: Wei Yang <richard.weiyang@xxxxxxxxxxxxxxxxx> > >>>> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > >>>> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> > >>>> Link: https://lore.kernel.org/r/20201112133815.13332-28-david@xxxxxxxxxx > >>>> Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx> > >>>> Acked-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > >>>> Signed-off-by: Ma Wupeng <mawupeng1@xxxxxxxxxx> > >>>> --- > >>>> mm/memory_hotplug.c | 105 +++++++++++++++++++++++++++++++++++++------- > >>>> 1 file changed, 89 insertions(+), 16 deletions(-) > >>>> > >>> > >>> Why is this needed in 5.10.y? Looks like a new feature to me, what > >>> problem does it solve there? > >>> > >>> thanks, > >>> > >>> greg k-h > >> > >> It do introduce a new feature. But at the same time, it fix a memleak introduced > >> in Commit 08b3acd7a68f ("mm/memory_hotplug: Introduce offline_and_remove_memory()" > >> > >> Our test find a memleak in init_memory_block, it is clear that mem is never > >> been released due to wrong refcount. Commit 08b3acd7a68f ("mm/memory_hotplug: > >> Introduce offline_and_remove_memory()") failed to dec refcount after > >> find_memory_block which fail to dec refcount to zero in remove memory > >> causing the leak. > >> > >> Commit 8dc4bb58a146 ("mm/memory_hotplug: extend offline_and_remove_memory() > >> to handle more than one memory block") introduce walk_memory_blocks to > >> replace find_memory_block which dec refcount by calling put_device after > >> find_memory_block_by_id. In the way, the memleak is fixed. > >> > >> Here is the simplified calltrace: > >> > >> kmem_cache_alloc_trace+0x664/0xed0 > >> init_memory_block+0x8c/0x170 > >> create_memory_block_devices+0xa4/0x150 > >> add_memory_resource+0x188/0x530 > >> __add_memory+0x78/0x104 > >> add_memory+0x6c/0xb0 > >> > > > > Makes sense to me. Of course, we could think about a simplified stable fix that only drops the ref. > > Since the new patch does not introduce any kabi change, maybe we can merge this one？ stable kernels never care about "kabi", that is a made up thing that some distros work to enforce only. It has nothing to do with the community. And I will always prefer to take the real commit that is in Linus's tree over any "custom" patch, as 90%+ of the time, custom changes are almost always wrong. thanks, greg k-h
