Currently there is no way to find out current layout of non-linear mapping.
Also there is no way to distinguish ordinary file mapping from non-linear mapping.
Now in pagemap non-linear pte can be recognized as present swapped file-backed,
or as non-present non-swapped file-backed for non-present non-linear file-pte:
present swapped file data description
0 0 0 null non-present
0 0 1 page-index non-linear file-pte
0 1 0 swap-entry anon-page in swap, migration or hwpoison
0 1 1 swap-entry file-page in migration or hwpoison
1 0 0 page-pfn present private-anon or special page
1 0 1 page-pfn present file or shared-anon page
1 1 0 none impossible combination
1 1 1 page-index non-linear file-page
[ the last unused combination 1-1-0 can be used for special pages, if anyone want this ]
Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxx>
Cc: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
---
Documentation/vm/pagemap.txt | 15 +++++++++++++++
fs/proc/task_mmu.c | 13 +++++++++++--
2 files changed, 26 insertions(+), 2 deletions(-)
diff --git a/Documentation/vm/pagemap.txt b/Documentation/vm/pagemap.txt
index 7587493..6800dda 100644
--- a/Documentation/vm/pagemap.txt
+++ b/Documentation/vm/pagemap.txt
@@ -13,6 +13,7 @@ There are three components to pagemap:
fs/proc/task_mmu.c, above pagemap_read):
* Bits 0-54 page frame number (PFN) if present
+ * Bits 0-54 page index for non-linear mappings
* Bits 0-4 swap type if swapped
* Bits 5-54 swap offset if swapped
* Bits 55-60 page shift (page size = 1<<page shift)
@@ -26,6 +27,20 @@ There are three components to pagemap:
precisely which pages are mapped (or in swap) and comparing mapped
pages between processes.
+ For non-linear file mappings page index is reported instead of PFN.
+ Non-linear pte can be recognized as present swapped file-backed or
+ non-present non-swapped file-backed.
+
+ present swapped file data description
+ 0 0 0 null non-present
+ 0 0 1 page-index non-linear file-pte
+ 0 1 0 swap-entry anon-page in swap, migration or hwpoison
+ 0 1 1 swap-entry file-page in migration or hwpoison
+ 1 0 0 page-pfn present private-anon or special page
+ 1 0 1 page-pfn present file or shared-anon page
+ 1 1 0 none impossible combination
+ 1 1 1 page-index non-linear file-page
+
Efficient users of this interface will use /proc/pid/maps to
determine which areas of memory are actually mapped and llseek to
skip over unmapped regions.
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index bc3df31..fcc802f 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -744,6 +744,9 @@ static void pte_to_pagemap_entry(pagemap_entry_t *pme,
frame = pte_pfn(pte);
flags = PM_PRESENT;
page = vm_normal_page(vma, addr, pte);
+ } if (pte_file(pte)) {
+ frame = pte_to_pgoff(pte);
+ flags = PM_FILE;
} if (is_swap_pte(pte)) {
swp_entry_t entry = pte_to_swp_entry(pte);
@@ -755,8 +758,13 @@ static void pte_to_pagemap_entry(pagemap_entry_t *pme,
} else
return;
- if (page && !PageAnon(page))
- flags |= PM_FILE;
+ if (page) {
+ if (vma->vm_flags & VM_NONLINEAR) {
+ frame = page->index;
+ flags = PM_FILE | PM_SWAP | PM_PRESENT;
+ } else if (!PageAnon(page))
+ flags |= PM_FILE;
+ }
*pme = make_pme(PM_PFRAME(frame) | PM_PSHIFT(PAGE_SHIFT) | flags);
}
@@ -874,6 +882,7 @@ static int pagemap_hugetlb_range(pte_t *pte, unsigned long hmask,
* consisting of the following:
*
* Bits 0-54 page frame number (PFN) if present
+ * Bits 0-54 page index for non-linear mappings
* Bits 0-4 swap type if swapped
* Bits 5-54 swap offset if swapped
* Bits 55-60 page shift (page size = 1<<page shift)
--
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