Re: [PATCH v1] mm/madvise: update comment on sys_madvise()

[Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>]

On Wed, Jan 27, 2016 at 04:28:35PM +0100, Michal Hocko wrote:
> On Wed 27-01-16 10:24:25, Naoya Horiguchi wrote:
> > Some new MADV_* advices are not documented in sys_madvise() comment.
> > So let's update it.
> > 
> > Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> 
> Other than few suggestions below
> Acked-by: Michal Hocko <mhocko@suse.com>
> 
> > ---
> >  mm/madvise.c | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> > 
> > diff --git v4.4-mmotm-2016-01-20-16-10/mm/madvise.c v4.4-mmotm-2016-01-20-16-10_patched/mm/madvise.c
> > index 6a77114..c897b15 100644
> > --- v4.4-mmotm-2016-01-20-16-10/mm/madvise.c
> > +++ v4.4-mmotm-2016-01-20-16-10_patched/mm/madvise.c
> > @@ -639,14 +639,26 @@ madvise_behavior_valid(int behavior)
> >   *		some pages ahead.
> >   *  MADV_DONTNEED - the application is finished with the given range,
> >   *		so the kernel can free resources associated with it.
> > + *  MADV_FREE - the application marks pages in the given range as lasyfree,
> 
> s@lasyfree@lazy free@
> 
> > + *		where actual purges are postponed until memory pressure happens.
> >   *  MADV_REMOVE - the application wants to free up the given range of
> >   *		pages and associated backing store.
> >   *  MADV_DONTFORK - omit this area from child's address space when forking:
> >   *		typically, to avoid COWing pages pinned by get_user_pages().
> >   *  MADV_DOFORK - cancel MADV_DONTFORK: no longer omit this area when forking.
> > + *  MADV_HWPOISON - trigger memory error handler as if the given memory range
> > + *		were corrupted by unrecoverable hardware memory failure.
> > + *  MADV_SOFT_OFFLINE - try to soft-offline the given range of memory.
> >   *  MADV_MERGEABLE - the application recommends that KSM try to merge pages in
> >   *		this area with pages of identical content from other such areas.
> >   *  MADV_UNMERGEABLE- cancel MADV_MERGEABLE: no longer merge pages with others.
> > + *  MADV_HUGEPAGE - the application wants to allocate transparent hugepages to
> > + *		load the content of the given memory range.
> 
> I guess that a slightly different wording would be better:
> 
> application wants to back the given range by transparent huge pages in
> the future. Existing pages might be coalesced and new pages might be
> allocated as THP.
> 
> > + *  MADV_NOHUGEPAGE - cancel MADV_HUGEPAGE: no longer allocate transparent
> > + *		hugepages.
> 
> Mark the given range as not worth being backed by transparent huge pages
> so neither existing pages will be coalesced into THP nor new pages will
> be allocated as THP.

Thank you for the elaboration.
I'm fine for all these change.

- Naoya
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