Commit f6b3ec23 authored by Badari Pulavarty's avatar Badari Pulavarty Committed by Linus Torvalds
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[PATCH] madvise(MADV_REMOVE): remove pages from tmpfs shm backing store



Here is the patch to implement madvise(MADV_REMOVE) - which frees up a
given range of pages & its associated backing store.  Current
implementation supports only shmfs/tmpfs and other filesystems return
-ENOSYS.

"Some app allocates large tmpfs files, then when some task quits and some
client disconnect, some memory can be released.  However the only way to
release tmpfs-swap is to MADV_REMOVE". - Andrea Arcangeli

Databases want to use this feature to drop a section of their bufferpool
(shared memory segments) - without writing back to disk/swap space.

This feature is also useful for supporting hot-plug memory on UML.

Concerns raised by Andrew Morton:

- "We have no plan for holepunching!  If we _do_ have such a plan (or
  might in the future) then what would the API look like?  I think
  sys_holepunch(fd, start, len), so we should start out with that."

- Using madvise is very weird, because people will ask "why do I need to
  mmap my file before I can stick a hole in it?"

- None of the other madvise operations call into the filesystem in this
  manner.  A broad question is: is this capability an MM operation or a
  filesytem operation?  truncate, for example, is a filesystem operation
  which sometimes has MM side-effects.  madvise is an mm operation and with
  this patch, it gains FS side-effects, only they're really, really
  significant ones."

Comments:

- Andrea suggested the fs operation too but then it's more efficient to
  have it as a mm operation with fs side effects, because they don't
  immediatly know fd and physical offset of the range.  It's possible to
  fixup in userland and to use the fs operation but it's more expensive,
  the vmas are already in the kernel and we can use them.

Short term plan &  Future Direction:

- We seem to need this interface only for shmfs/tmpfs files in the short
  term.  We have to add hooks into the filesystem for correctness and
  completeness.  This is what this patch does.

- In the future, plan is to support both fs and mmap apis also.  This
  also involves (other) filesystem specific functions to be implemented.

- Current patch doesn't support VM_NONLINEAR - which can be addressed in
  the future.
Signed-off-by: default avatarBadari Pulavarty <pbadari@us.ibm.com>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: Andrea Arcangeli <andrea@suse.de>
Cc: Michael Kerrisk <mtk-manpages@gmx.net>
Cc: Ulrich Drepper <drepper@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent d7339071
......@@ -42,6 +42,7 @@
#define MADV_WILLNEED 3 /* will need these pages */
#define MADV_SPACEAVAIL 5 /* ensure resources are available */
#define MADV_DONTNEED 6 /* don't need these pages */
#define MADV_REMOVE 7 /* remove these pages & resources */
/* compatibility flags */
#define MAP_ANON MAP_ANONYMOUS
......
......@@ -35,6 +35,7 @@
#define MADV_SEQUENTIAL 0x2 /* read-ahead aggressively */
#define MADV_WILLNEED 0x3 /* pre-fault pages */
#define MADV_DONTNEED 0x4 /* discard these pages */
#define MADV_REMOVE 0x5 /* remove these pages & resources */
/* compatibility flags */
#define MAP_ANON MAP_ANONYMOUS
......
......@@ -35,6 +35,7 @@
#define MADV_SEQUENTIAL 0x2 /* read-ahead aggressively */
#define MADV_WILLNEED 0x3 /* pre-fault pages */
#define MADV_DONTNEED 0x4 /* discard these pages */
#define MADV_REMOVE 0x5 /* remove these pages & resources */
/* compatibility flags */
#define MAP_ANON MAP_ANONYMOUS
......
......@@ -37,6 +37,7 @@
#define MADV_SEQUENTIAL 0x2 /* read-ahead aggressively */
#define MADV_WILLNEED 0x3 /* pre-fault pages */
#define MADV_DONTNEED 0x4 /* discard these pages */
#define MADV_REMOVE 0x5 /* remove these pages & resources */
/* compatibility flags */
#define MAP_ANON MAP_ANONYMOUS
......
......@@ -35,6 +35,7 @@
#define MADV_SEQUENTIAL 0x2 /* read-ahead aggressively */
#define MADV_WILLNEED 0x3 /* pre-fault pages */
#define MADV_DONTNEED 0x4 /* discard these pages */
#define MADV_REMOVE 0x5 /* remove these pages & resources */
/* compatibility flags */
#define MAP_ANON MAP_ANONYMOUS
......
......@@ -35,6 +35,7 @@
#define MADV_SEQUENTIAL 0x2 /* read-ahead aggressively */
#define MADV_WILLNEED 0x3 /* pre-fault pages */
#define MADV_DONTNEED 0x4 /* discard these pages */
#define MADV_REMOVE 0x5 /* remove these pages & resources */
/* compatibility flags */
#define MAP_ANON MAP_ANONYMOUS
......
......@@ -35,6 +35,7 @@
#define MADV_SEQUENTIAL 0x2 /* read-ahead aggressively */
#define MADV_WILLNEED 0x3 /* pre-fault pages */
#define MADV_DONTNEED 0x4 /* discard these pages */
#define MADV_REMOVE 0x5 /* remove these pages & resources */
/* compatibility flags */
#define MAP_ANON MAP_ANONYMOUS
......
......@@ -43,6 +43,7 @@
#define MADV_SEQUENTIAL 0x2 /* read-ahead aggressively */
#define MADV_WILLNEED 0x3 /* pre-fault pages */
#define MADV_DONTNEED 0x4 /* discard these pages */
#define MADV_REMOVE 0x5 /* remove these pages & resources */
/* compatibility flags */
#define MAP_ANON MAP_ANONYMOUS
......
......@@ -37,6 +37,7 @@
#define MADV_SEQUENTIAL 0x2 /* read-ahead aggressively */
#define MADV_WILLNEED 0x3 /* pre-fault pages */
#define MADV_DONTNEED 0x4 /* discard these pages */
#define MADV_REMOVE 0x5 /* remove these pages & resources */
/* compatibility flags */
#define MAP_ANON MAP_ANONYMOUS
......
......@@ -35,6 +35,7 @@
#define MADV_SEQUENTIAL 0x2 /* read-ahead aggressively */
#define MADV_WILLNEED 0x3 /* pre-fault pages */
#define MADV_DONTNEED 0x4 /* discard these pages */
#define MADV_REMOVE 0x5 /* remove these pages & resources */
/* compatibility flags */
#define MAP_ANON MAP_ANONYMOUS
......
......@@ -65,6 +65,7 @@
#define MADV_SEQUENTIAL 0x2 /* read-ahead aggressively */
#define MADV_WILLNEED 0x3 /* pre-fault pages */
#define MADV_DONTNEED 0x4 /* discard these pages */
#define MADV_REMOVE 0x5 /* remove these pages & resources */
/* compatibility flags */
#define MAP_ANON MAP_ANONYMOUS
......
......@@ -38,6 +38,7 @@
#define MADV_SPACEAVAIL 5 /* insure that resources are reserved */
#define MADV_VPS_PURGE 6 /* Purge pages from VM page cache */
#define MADV_VPS_INHERIT 7 /* Inherit parents page size */
#define MADV_REMOVE 8 /* remove these pages & resources */
/* The range 12-64 is reserved for page size specification. */
#define MADV_4K_PAGES 12 /* Use 4K pages */
......
......@@ -44,6 +44,7 @@
#define MADV_SEQUENTIAL 0x2 /* read-ahead aggressively */
#define MADV_WILLNEED 0x3 /* pre-fault pages */
#define MADV_DONTNEED 0x4 /* discard these pages */
#define MADV_REMOVE 0x5 /* remove these pages & resources */
/* compatibility flags */
#define MAP_ANON MAP_ANONYMOUS
......
......@@ -43,6 +43,7 @@
#define MADV_SEQUENTIAL 0x2 /* read-ahead aggressively */
#define MADV_WILLNEED 0x3 /* pre-fault pages */
#define MADV_DONTNEED 0x4 /* discard these pages */
#define MADV_REMOVE 0x5 /* remove these pages & resources */
/* compatibility flags */
#define MAP_ANON MAP_ANONYMOUS
......
......@@ -35,6 +35,7 @@
#define MADV_SEQUENTIAL 0x2 /* read-ahead aggressively */
#define MADV_WILLNEED 0x3 /* pre-fault pages */
#define MADV_DONTNEED 0x4 /* discard these pages */
#define MADV_REMOVE 0x5 /* remove these pages & resources */
/* compatibility flags */
#define MAP_ANON MAP_ANONYMOUS
......
......@@ -54,6 +54,7 @@
#define MADV_WILLNEED 0x3 /* pre-fault pages */
#define MADV_DONTNEED 0x4 /* discard these pages */
#define MADV_FREE 0x5 /* (Solaris) contents can be freed */
#define MADV_REMOVE 0x6 /* remove these pages & resources */
/* compatibility flags */
#define MAP_ANON MAP_ANONYMOUS
......
......@@ -54,6 +54,7 @@
#define MADV_WILLNEED 0x3 /* pre-fault pages */
#define MADV_DONTNEED 0x4 /* discard these pages */
#define MADV_FREE 0x5 /* (Solaris) contents can be freed */
#define MADV_REMOVE 0x6 /* remove these pages & resources */
/* compatibility flags */
#define MAP_ANON MAP_ANONYMOUS
......
......@@ -32,6 +32,7 @@
#define MADV_SEQUENTIAL 0x2 /* read-ahead aggressively */
#define MADV_WILLNEED 0x3 /* pre-fault pages */
#define MADV_DONTNEED 0x4 /* discard these pages */
#define MADV_REMOVE 0x5 /* remove these pages & resources */
/* compatibility flags */
#define MAP_ANON MAP_ANONYMOUS
......
......@@ -36,6 +36,7 @@
#define MADV_SEQUENTIAL 0x2 /* read-ahead aggressively */
#define MADV_WILLNEED 0x3 /* pre-fault pages */
#define MADV_DONTNEED 0x4 /* discard these pages */
#define MADV_REMOVE 0x5 /* remove these pages & resources */
/* compatibility flags */
#define MAP_ANON MAP_ANONYMOUS
......
......@@ -72,6 +72,7 @@
#define MADV_SEQUENTIAL 0x2 /* read-ahead aggressively */
#define MADV_WILLNEED 0x3 /* pre-fault pages */
#define MADV_DONTNEED 0x4 /* discard these pages */
#define MADV_REMOVE 0x5 /* remove these pages & resources */
/* compatibility flags */
#define MAP_ANON MAP_ANONYMOUS
......
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