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madvise.2: Tweaks and improvements to Minchan's text 

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
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Michael Kerrisk 2016-02-06 13:02:25 +01:00
parent 9ec1369898
commit d432f10d89
1 changed files with 26 additions and 13 deletions
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@ -362,21 +362,34 @@ file (see
Undo the effect of an earlier
.BR MADV_DONTDUMP .
.TP
.B MADV_FREE " (since Linux 4.5)"
Application is finished with the given range, so kernel can free
resources associated with it but the freeing could be delayed until
memory pressure happens or canceld by write operation by user.
.BR MADV_FREE " (since Linux 4.5)"
The application no longer requires the pages in the range specified by
.IR addr
and
.IR len .
The kernel can thus free these pages,
but the freeing could be delayed until memory pressure occurs.
For each of the pages that has been marked to be freed
but has not yet been freed,
the free operation will be canceled if the caller writes into the page.
After a successful
.B MADV_FREE
operation, any stale data (i.e., dirty, unwritten pages) will be lost
when the kernel frees the pages.
However, subsequent writes to pages in the range will succeed
and then kernel cannot free those dirtied pages,
so that the caller can always see just written data.
If there is no subsequent write,
the kernel can free the pages at any time.
Once pages in the range have been freed, the caller will
see zero-fill-on-demand pages upon subsequent page references.
After a successful MADV_FREE operation, user shouldn't expect kernel
keeps stale data on the page. However, subsequent write of pages
in the range will succeed and then kernel cannot free those dirtied pages
so user can always see just written data. If there was no subsequent
write, kernel can free those clean pages any time. In such case,
user can see zero-fill-on-demand pages.
Note that, it works only with private anonymous pages (see
The
.B MADV_FREE
operation
can be applied only to private anonymous pages (see
.BR mmap (2)).
On swapless system, freeing pages in given range happens instantly
On a swapless system, freeing pages in a given range happens instantly,
regardless of memory pressure.
.SH RETURN VALUE
On success,