Hello Michal, On Thu, Nov 27, 2014 at 03:47:25PM +0100, Michal Hocko wrote: > [Late but I didn't get to this soone - I hope this is still up-to-date > version] > > On Mon 20-10-14 19:11:58, Minchan Kim wrote: > > Linux doesn't have an ability to free pages lazy while other OS > > already have been supported that named by madvise(MADV_FREE). > > > > The gain is clear that kernel can discard freed pages rather than > > swapping out or OOM if memory pressure happens. > > > > Without memory pressure, freed pages would be reused by userspace > > without another additional overhead(ex, page fault + allocation > > + zeroing). > > > > How to work is following as. > > > > When madvise syscall is called, VM clears dirty bit of ptes of > > the range. If memory pressure happens, VM checks dirty bit of > > page table and if it found still "clean", it means it's a > > "lazyfree pages" so VM could discard the page instead of swapping out. > > Once there was store operation for the page before VM peek a page > > to reclaim, dirty bit is set so VM can swap out the page instead of > > discarding. > > Is there any patch for madvise man page? I guess the semantic will be > same/similar to FreeBSD: > http://www.freebsd.org/cgi/man.cgi?query=madvise&sektion=2 I postponed because I didn't know when we release the feature into mainline but I should write down in man page ("MADV_FREE since Linux x.x.x"). However, early posting is not harmful. Here it goes. Most of content was copied from FreeBSD man page. >From 2edd6890f92fa4943ce3c452194479458582d88c Mon Sep 17 00:00:00 2001 From: Minchan Kim <minchan@xxxxxxxxxx> Date: Mon, 1 Dec 2014 08:53:55 +0900 Subject: [PATCH] madvise.2: Document MADV_FREE 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 > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@xxxxxxxxx. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>