Am 6/17/22 um 23:19 schrieb David Hildenbrand:
On 17.06.22 21:27, Sierra Guiza, Alejandro (Alex) wrote:
On 6/17/2022 12:33 PM, David Hildenbrand wrote:
On 17.06.22 19:20, Sierra Guiza, Alejandro (Alex) wrote:
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@xxxxxxx>
Acked-by: Felix Kuehling <Felix.Kuehling@xxxxxxx>
Reviewed-by: Alistair Popple <apopple@xxxxxxxxxx>
[hch: rebased ontop of the refcount changes,
removed is_dev_private_or_coherent_page]
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
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 ...
Well, you cannot migrate long term pages, that's what I meant :)
+ * 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.
I don't see updates to folio_is_pinnable() in this patch.
Device coherent type pages should return true here, as they are pinnable
pages.
That function is only called for long-term pinnings in try_grab_folio().
So wouldn't try_grab_folio() simply pin these pages? What am I missing?
As far as I understand this return NULL for long term pin pages.
Otherwise they get refcount incremented.
I don't follow.
You're saying
a) folio_is_pinnable() returns true for device coherent pages
and that
b) device coherent pages don't get long-term pinned
Yet, the code says
struct folio *try_grab_folio(struct page *page, int refs, unsigned int flags)
{
if (flags & FOLL_GET)
return try_get_folio(page, refs);
else if (flags & FOLL_PIN) {
struct folio *folio;
/*
* Can't do FOLL_LONGTERM + FOLL_PIN gup fast path if not in a
* right zone, so fail and let the caller fall back to the slow
* path.
*/
if (unlikely((flags & FOLL_LONGTERM) &&
!is_pinnable_page(page)))
return NULL;
...
return folio;
}
}
What prevents these pages from getting long-term pinned as stated in this patch?
Long-term pinning is handled by __gup_longterm_locked, which migrates
pages returned by __get_user_pages_locked that cannot be long-term
pinned. try_grab_folio is OK to grab the pages. Anything that can't be
long-term pinned will be migrated afterwards, and
__get_user_pages_locked will be retried. The migration of
DEVICE_COHERENT pages was implemented by Alistair in patch 5/13
("mm/gup: migrate device coherent pages when pinning instead of failing").
Regards,
Felix
I am probably missing something important.
P.S.: I'm on vacation and looking at a tiny screen. Hope I didn't miss
anything myself.
