[PATCH] madvise.2: Document MADV_FREE

[Minchan Kim]

Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
 man2/madvise.2 | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/man2/madvise.2 b/man2/madvise.2
index 032ead7..33aa936 100644
--- a/man2/madvise.2
+++ b/man2/madvise.2
@@ -265,6 +265,19 @@ file (see
 .BR MADV_DODUMP " (since Linux 3.4)"
 Undo the effect of an earlier
 .BR MADV_DONTDUMP .
+.TP
+.BR MADV_FREE " (since Linux 3.19)"
+Gives the VM system the freedom to free pages, and tells the system that
+information in the specified page range is no longer important.
+This is an efficient way of allowing
+.BR malloc (3)
+to free pages anywhere in the address space, while keeping the address space
+valid. The next time that the page is referenced, the page might be demand
+zeroed, or might contain the data that was there before the MADV_FREE call.
+References made to that address space range will not make the VM system page the
+information back in from backing store until the page is modified again.
+It works only with private anonymous pages (see
+.BR mmap (2)).
 .SH RETURN VALUE
 On success
 .BR madvise ()
-- 
2.0.0


> 
> I guess the changelog should be more specific that this is only for the
> private MAP_ANON mappings (same applies to the patch for man).
> 
> > Firstly, heavy users would be general allocators(ex, jemalloc,
> > tcmalloc and hope glibc supports it) and jemalloc/tcmalloc already
> > have supported the feature for other OS(ex, FreeBSD)
> > 
> [...]
> > 
> > Cc: Michael Kerrisk <mtk.manpages@xxxxxxxxx>
> > Cc: Linux API <linux-api@xxxxxxxxxxxxxxx>
> > Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> > Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> > Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> > Cc: Mel Gorman <mgorman@xxxxxxx>
> > Cc: Jason Evans <je@xxxxxx>
> > Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> > Acked-by: Zhang Yanfei <zhangyanfei@xxxxxxxxxxxxxx>
> > Acked-by: Rik van Riel <riel@xxxxxxxxxx>
> > Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
> 
> Reviewed-by: Michal Hocko <mhocko@xxxxxxx>
> [...]
> -- 
> Michal Hocko
> SUSE Labs
> 
> --
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-- 
Kind regards,
Minchan Kim
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