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authorHugh Dickins <hughd@google.com>2015-11-06 05:49:30 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2015-11-06 06:34:48 +0300
commit7a14239a8fff45a241b6943a3ac444d5b67fcbed (patch)
tree0877d45168aaf6e65dc86cc1d4f965fa03159077 /Documentation/vm/unevictable-lru.txt
parent706874e9096e9d468eed9c2b03c8374e806535f3 (diff)
downloadlinux-7a14239a8fff45a241b6943a3ac444d5b67fcbed.tar.xz
mm Documentation: undoc non-linear vmas
While updating some mm Documentation, I came across a few straggling references to the non-linear vmas which were happily removed in v4.0. Delete them. Signed-off-by: Hugh Dickins <hughd@google.com> Cc: Christoph Lameter <cl@linux.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Rik van Riel <riel@redhat.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Sasha Levin <sasha.levin@oracle.com> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/vm/unevictable-lru.txt')
-rw-r--r--Documentation/vm/unevictable-lru.txt63
1 files changed, 5 insertions, 58 deletions
diff --git a/Documentation/vm/unevictable-lru.txt b/Documentation/vm/unevictable-lru.txt
index 32ee3a67dba2..e983ee4e2758 100644
--- a/Documentation/vm/unevictable-lru.txt
+++ b/Documentation/vm/unevictable-lru.txt
@@ -552,63 +552,17 @@ different reverse map mechanisms.
is really unevictable or not. In this case, try_to_unmap_anon() will
return SWAP_AGAIN.
- (*) try_to_unmap_file() - linear mappings
+ (*) try_to_unmap_file()
Unmapping of a mapped file page works the same as for anonymous mappings,
except that the scan visits all VMAs that map the page's index/page offset
- in the page's mapping's reverse map priority search tree. It also visits
- each VMA in the page's mapping's non-linear list, if the list is
- non-empty.
+ in the page's mapping's reverse map interval search tree.
As for anonymous pages, on encountering a VM_LOCKED VMA for a mapped file
page, try_to_unmap_file() will attempt to acquire the associated
mm_struct's mmap semaphore to mlock the page, returning SWAP_MLOCK if this
is successful, and SWAP_AGAIN, if not.
- (*) try_to_unmap_file() - non-linear mappings
-
- If a page's mapping contains a non-empty non-linear mapping VMA list, then
- try_to_un{map|lock}() must also visit each VMA in that list to determine
- whether the page is mapped in a VM_LOCKED VMA. Again, the scan must visit
- all VMAs in the non-linear list to ensure that the pages is not/should not
- be mlocked.
-
- If a VM_LOCKED VMA is found in the list, the scan could terminate.
- However, there is no easy way to determine whether the page is actually
- mapped in a given VMA - either for unmapping or testing whether the
- VM_LOCKED VMA actually pins the page.
-
- try_to_unmap_file() handles non-linear mappings by scanning a certain
- number of pages - a "cluster" - in each non-linear VMA associated with the
- page's mapping, for each file mapped page that vmscan tries to unmap. If
- this happens to unmap the page we're trying to unmap, try_to_unmap() will
- notice this on return (page_mapcount(page) will be 0) and return
- SWAP_SUCCESS. Otherwise, it will return SWAP_AGAIN, causing vmscan to
- recirculate this page. We take advantage of the cluster scan in
- try_to_unmap_cluster() as follows:
-
- For each non-linear VMA, try_to_unmap_cluster() attempts to acquire the
- mmap semaphore of the associated mm_struct for read without blocking.
-
- If this attempt is successful and the VMA is VM_LOCKED,
- try_to_unmap_cluster() will retain the mmap semaphore for the scan;
- otherwise it drops it here.
-
- Then, for each page in the cluster, if we're holding the mmap semaphore
- for a locked VMA, try_to_unmap_cluster() calls mlock_vma_page() to
- mlock the page. This call is a no-op if the page is already locked,
- but will mlock any pages in the non-linear mapping that happen to be
- unlocked.
-
- If one of the pages so mlocked is the page passed in to try_to_unmap(),
- try_to_unmap_cluster() will return SWAP_MLOCK, rather than the default
- SWAP_AGAIN. This will allow vmscan to cull the page, rather than
- recirculating it on the inactive list.
-
- Again, if try_to_unmap_cluster() cannot acquire the VMA's mmap sem, it
- returns SWAP_AGAIN, indicating that the page is mapped by a VM_LOCKED
- VMA, but couldn't be mlocked.
-
try_to_munlock() REVERSE MAP SCAN
---------------------------------
@@ -625,10 +579,9 @@ introduced a variant of try_to_unmap() called try_to_munlock().
try_to_munlock() calls the same functions as try_to_unmap() for anonymous and
mapped file pages with an additional argument specifying unlock versus unmap
processing. Again, these functions walk the respective reverse maps looking
-for VM_LOCKED VMAs. When such a VMA is found for anonymous pages and file
-pages mapped in linear VMAs, as in the try_to_unmap() case, the functions
-attempt to acquire the associated mmap semaphore, mlock the page via
-mlock_vma_page() and return SWAP_MLOCK. This effectively undoes the
+for VM_LOCKED VMAs. When such a VMA is found, as in the try_to_unmap() case,
+the functions attempt to acquire the associated mmap semaphore, mlock the page
+via mlock_vma_page() and return SWAP_MLOCK. This effectively undoes the
pre-clearing of the page's PG_mlocked done by munlock_vma_page.
If try_to_unmap() is unable to acquire a VM_LOCKED VMA's associated mmap
@@ -636,12 +589,6 @@ semaphore, it will return SWAP_AGAIN. This will allow shrink_page_list() to
recycle the page on the inactive list and hope that it has better luck with the
page next time.
-For file pages mapped into non-linear VMAs, the try_to_munlock() logic works
-slightly differently. On encountering a VM_LOCKED non-linear VMA that might
-map the page, try_to_munlock() returns SWAP_AGAIN without actually mlocking the
-page. munlock_vma_page() will just leave the page unlocked and let vmscan deal
-with it - the usual fallback position.
-
Note that try_to_munlock()'s reverse map walk must visit every VMA in a page's
reverse map to determine that a page is NOT mapped into any VM_LOCKED VMA.
However, the scan can terminate when it encounters a VM_LOCKED VMA and can