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Date: Fri, 17 Jun 2022 12:20:46 -0500 From: "Sierra Guiza, Alejandro (Alex)" <alex.sierra@....com> To: David Hildenbrand <david@...hat.com>, jgg@...dia.com Cc: Felix.Kuehling@....com, linux-mm@...ck.org, rcampbell@...dia.com, linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org, amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org, hch@....de, jglisse@...hat.com, apopple@...dia.com, willy@...radead.org, akpm@...ux-foundation.org Subject: Re: [PATCH v5 01/13] mm: add zone device coherent type memory support On 6/17/2022 4:40 AM, David Hildenbrand wrote: > On 31.05.22 22:00, Alex Sierra wrote: >> Device memory that is cache coherent from device and CPU point of view. >> This is used on platforms that have an advanced system bus (like CAPI >> or CXL). Any page of a process can be migrated to such memory. However, >> no one should be allowed to pin such memory so that it can always be >> evicted. >> >> Signed-off-by: Alex Sierra <alex.sierra@....com> >> Acked-by: Felix Kuehling <Felix.Kuehling@....com> >> Reviewed-by: Alistair Popple <apopple@...dia.com> >> [hch: rebased ontop of the refcount changes, >> removed is_dev_private_or_coherent_page] >> Signed-off-by: Christoph Hellwig <hch@....de> >> --- >> include/linux/memremap.h | 19 +++++++++++++++++++ >> mm/memcontrol.c | 7 ++++--- >> mm/memory-failure.c | 8 ++++++-- >> mm/memremap.c | 10 ++++++++++ >> mm/migrate_device.c | 16 +++++++--------- >> mm/rmap.c | 5 +++-- >> 6 files changed, 49 insertions(+), 16 deletions(-) >> >> diff --git a/include/linux/memremap.h b/include/linux/memremap.h >> index 8af304f6b504..9f752ebed613 100644 >> --- a/include/linux/memremap.h >> +++ b/include/linux/memremap.h >> @@ -41,6 +41,13 @@ struct vmem_altmap { >> * A more complete discussion of unaddressable memory may be found in >> * include/linux/hmm.h and Documentation/vm/hmm.rst. >> * >> + * MEMORY_DEVICE_COHERENT: >> + * Device memory that is cache coherent from device and CPU point of view. This >> + * is used on platforms that have an advanced system bus (like CAPI or CXL). A >> + * driver can hotplug the device memory using ZONE_DEVICE and with that memory >> + * type. Any page of a process can be migrated to such memory. However no one > Any page might not be right, I'm pretty sure. ... just thinking about special pages > like vdso, shared zeropage, ... pinned pages ... Hi David, Yes, I think you're right. This type does not cover all special pages. I need to correct that on the cover letter. Pinned pages are allowed as long as they're not long term pinned. Regards, Alex Sierra > >> + * should be allowed to pin such memory so that it can always be evicted. >> + * >> * MEMORY_DEVICE_FS_DAX: >> * Host memory that has similar access semantics as System RAM i.e. DMA >> * coherent and supports page pinning. In support of coordinating page >> @@ -61,6 +68,7 @@ struct vmem_altmap { >> enum memory_type { >> /* 0 is reserved to catch uninitialized type fields */ >> MEMORY_DEVICE_PRIVATE = 1, >> + MEMORY_DEVICE_COHERENT, >> MEMORY_DEVICE_FS_DAX, >> MEMORY_DEVICE_GENERIC, >> MEMORY_DEVICE_PCI_P2PDMA, >> @@ -143,6 +151,17 @@ static inline bool folio_is_device_private(const struct folio *folio) > In general, this LGTM, and it should be correct with PageAnonExclusive I think. > > > However, where exactly is pinning forbidden? Long-term pinning is forbidden since it would interfere with the device memory manager owning the device-coherent pages (e.g. evictions in TTM). However, normal pinning is allowed on this device type. Regards, Alex Sierra >
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