LDP
/
man-pages
mirror of https://github.com/mkerrisk/man-pages
0
1
Fork 0
Code Releases Activity

Document MADV_REMOVE. 

Document MADV_DONTFORK / MADV_DOFORK.
This commit is contained in:
Michael Kerrisk 2006-09-05 11:47:03 +00:00
parent 78cb591178
commit 835c4d5ce4
1 changed files with 51 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

52
man2/madvise.2
View File

@ -28,7 +28,6 @@
.\"
.\" FIXME 2.6.16 added MADV_REMOVE, MADV_DONTFORK, and MADV_DOFORK.
.\" These need to be documented.
.\" MADV_REMOVE /* remove these pages & resources */
.\" MADV_DONTFORK /* don't inherit across fork */
.\" MADV_DOFORK /* do inherit across fork */
.\" A discussion of MADV_DONTFORK and MADV_DOFORK can be found
@ -87,6 +86,51 @@ Subsequent accesses of pages in this range will succeed, but will result
either in re-loading of the memory contents from the underlying mapped file
(see \fBmmap\fP()) or zero-fill-on-demand pages for mappings
without an underlying file.
.TP
.BR MADV_REMOVE " (Since Linux 2.6.16)"
Free up a given range of pages
and its associated backing store.
Currently,
.\" 2.6.18-rc5
only shmfs/tmpfs supports this; other filesystems return -ENOSYS.
.\" 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.
.TP
.BR MADV_DONTFORK " (Since Linux 2.6.16)"
.\" See http://lwn.net/Articles/171941/
Do not make the pages in this range available to the child after a
.BR fork (2).
This is useful to prevent copy-on-write semantics from changing
the physical location of a pagei(s) if the parent writes to it after a
.BR fork (2).
(Such page relocations cause problems for hardware that
DMAs into the page(s).)
.\" [PATCH] madvise MADV_DONTFORK/MADV_DOFORK
.\" Currently, copy-on-write may change the physical address of
.\" a page even if the user requested that the page is pinned in
.\" memory (either by mlock or by get_user_pages). This happens
.\" if the process forks meanwhile, and the parent writes to that
.\" page. As a result, the page is orphaned: in case of
.\" get_user_pages, the application will never see any data hardware
.\" DMA's into this page after the COW. In case of mlock'd memory,
.\" the parent is not getting the realtime/security benefits of mlock.
.\"
.\" In particular, this affects the Infiniband modules which do DMA from
.\" and into user pages all the time.
.\"
.\" This patch adds madvise options to control whether memory range is
.\" inherited across fork. Useful e.g. for when hardware is doing DMA
.\" from/into these pages. Could also be useful to an application
.\" wanting to speed up its forks by cutting large areas out of
.\" consideration.
.TP
.BR MADV_DOFORK " (Since Linux 2.6.16)"
Undo the effect of
.BR MADV_DONTFORK ,
restoring the default behaviour, whereby a mapping is inherited across
.BR fork (2).
.SH "RETURN VALUE"
On success
.BR madvise ()
@ -153,6 +197,12 @@ with constants POSIX_MADV_NORMAL, etc.,
with a behaviour close to that described here. There is a similar
.BR posix_fadvise ()
for file access.
.BR MADV_REMOVE ,
.BR MADV_DONTFORK ,
and
.BR MADV_DOFORK
are Linux specific.
.SH "SEE ALSO"
.BR getrlimit (2),
.BR mincore (2),