Re: [patch 13/15] mm/page_owner: align with pageblock_nr pages

[Michal Hocko <mhocko@suse.com>]

On Mon 04-12-17 20:23:49, zhong jiang wrote:
> On 2017/12/4 20:01, Michal Hocko wrote:
> > On Mon 04-12-17 19:51:12, zhong jiang wrote:
> >> On 2017/12/2 1:15, Michal Hocko wrote:
> >>> On Fri 01-12-17 17:58:28, Vlastimil Babka wrote:
> >>>> On 11/30/2017 11:15 PM, akpm@linux-foundation.org wrote:
> >>>>> From: zhong jiang <zhongjiang@huawei.com>
> >>>>> Subject: mm/page_owner: align with pageblock_nr pages
> >>>>>
> >>>>> When pfn_valid(pfn) returns false, pfn should be aligned with
> >>>>> pageblock_nr_pages other than MAX_ORDER_NR_PAGES in init_pages_in_zone,
> >>>>> because the skipped 2M may be valid pfn, as a result, early allocated
> >>>>> count will not be accurate.
> >>>>>
> >>>>> Link: http://lkml.kernel.org/r/1468938136-24228-1-git-send-email-zhongjiang@huawei.com
> >>>>> Signed-off-by: zhong jiang <zhongjiang@huawei.com>
> >>>>> Cc: Michal Hocko <mhocko@kernel.org>
> >>>>> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> >>>> The author never responded and Michal Hocko basically NAKed it in
> >>>> https://lkml.kernel.org/r/<20160812130727.GI3639@dhcp22.suse.cz>
> >>>> I think we should drop it.
> >>> Or extend the changelog to actually describe what kind of problem it
> >>> fixes and do an additional step to unigy
> >>> MAX_ORDER_NR_PAGES/pageblock_nr_pages
> >>>  
> >>   Hi, Michal
> >>    
> >>         IIRC,  I had explained the reason for patch.  if it not. I am so sorry for that.
> >>     
> >>         when we select MAX_ORDER_NR_PAGES,   the second 2M will be skiped.
> >>        it maybe result in normal pages leak.
> >>
> >>         meanwhile.  as you had said.  it make the code consistent.  why do not we do it.
> >>    
> >>         I think it is reasonable to upstream the patch.  maybe I should rewrite the changelog
> >>        and repost it.
> >>
> >>     Michal,  Do you think ?
> > Yes, rewrite the patch changelog and make it _clear_ what it fixes and
> > under _what_ conditions. There are also other places using
> > MAX_ORDER_NR_PAGES rathern than pageblock_nr_pages. Do they need to be
> > updated as well?
>  in the lastest kernel.  according to correspond context,   I  can not find the candidate. :-)

git grep says some in page_ext.c, memory_hotplug.c and few in the arch
code. I belive we really want to describe and document the distinction
between the two constants and explain when to use which one.

-- 
Michal Hocko
SUSE Labs

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