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mm, dax, pmem: introduce pfn_t

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For the purpose of communicating the optional presence of a 'struct
page' for the pfn returned from ->direct_access(), introduce a type that
encapsulates a page-frame-number plus flags.  These flags contain the
historical "page_link" encoding for a scatterlist entry, but can also
denote "device memory".  Where "device memory" is a set of pfns that are
not part of the kernel's linear mapping by default, but are accessed via
the same memory controller as ram.

The motivation for this new type is large capacity persistent memory
that needs struct page entries in the 'memmap' to support 3rd party DMA
(i.e.  O_DIRECT I/O with a persistent memory source/target).  However,
we also need it in support of maintaining a list of mapped inodes which
need to be unmapped at driver teardown or freeze_bdev() time.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dave Hansen <dave@sr71.net>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Dan Williams
2016-01-15 16:56:14 -08:00
committed by Linus Torvalds
parent ba049e93ae
commit 34c0fd540e
9 changed files with 116 additions and 23 deletions
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9
include/linux/pfn.h
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@@ -3,6 +3,15 @@
#ifndef __ASSEMBLY__
#include <linux/types.h>
/*
* pfn_t: encapsulates a page-frame number that is optionally backed
* by memmap (struct page). Whether a pfn_t has a 'struct page'
* backing is indicated by flags in the high bits of the value.
*/
typedef struct {
unsigned long val;
} pfn_t;
#endif
#define PFN_ALIGN(x) (((unsigned long)(x) + (PAGE_SIZE - 1)) & PAGE_MASK)