From: Michal Hocko <mhocko@kernel.org>
To: Oscar Salvador <osalvador@suse.de>
Cc: Wei Yang <richard.weiyang@gmail.com>,
akpm@linux-foundation.org, vbabka@suse.cz,
pavel.tatashin@microsoft.com, rppt@linux.vnet.ibm.com,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] mm, page_alloc: Fix has_unmovable_pages for HugePages
Date: Thu, 20 Dec 2018 15:39:39 +0100 [thread overview]
Message-ID: <20181220143939.GA6210@dhcp22.suse.cz> (raw)
In-Reply-To: <20181220142124.r34fnuv6b33luj5a@d104.suse.de>
On Thu 20-12-18 15:21:27, Oscar Salvador wrote:
> On Thu, Dec 20, 2018 at 02:41:32PM +0100, Oscar Salvador wrote:
> > On Thu, Dec 20, 2018 at 02:06:06PM +0100, Michal Hocko wrote:
> > > You did want iter += skip_pages - 1 here right?
> >
> > Bleh, yeah.
> > I am taking vacation today so my brain has left me hours ago, sorry.
> > Should be:
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 4812287e56a0..0634fbdef078 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -8094,7 +8094,7 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
> > goto unmovable;
> >
> > skip_pages = (1 << compound_order(head)) - (page - head);
> > - iter = round_up(iter + 1, skip_pages) - 1;
> > + iter += skip_pages - 1;
> > continue;
> > }
>
> On a second thought, I think it should not really matter.
>
> AFAICS, we can have these scenarios:
>
> 1) the head page is the first page in the pabeblock
> 2) first page in the pageblock is not a head but part of a hugepage
> 3) the head is somewhere within the pageblock
>
> For cases 1) and 3), iter will just get the right value and we will
> break the loop afterwards.
>
> In case 2), iter will be set to a value to skip over the remaining pages.
>
> I am assuming that hugepages are allocated and packed together.
>
> Note that I am not against the change, but I just wanted to see if there is
> something I am missing.
Yes, you are missing that this code should be as sane as possible ;) You
are right that we are only processing one pageorder worth of pfns and
that the page order is bound to HUGETLB_PAGE_ORDER _right_now_. But
there is absolutely zero reason to hardcode that assumption into a
simple loop, right?
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2018-12-20 14:39 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-17 22:51 [PATCH v2] mm, page_alloc: Fix has_unmovable_pages for HugePages Oscar Salvador
2018-12-17 23:07 ` Andrew Morton
2018-12-18 7:36 ` Michal Hocko
2018-12-18 21:46 ` Andrew Morton
2018-12-18 21:51 ` Oscar Salvador
2018-12-19 14:25 ` Wei Yang
2018-12-19 14:28 ` Wei Yang
2018-12-19 23:39 ` Oscar Salvador
2018-12-20 9:12 ` Michal Hocko
2018-12-20 12:49 ` Oscar Salvador
2018-12-20 13:06 ` Michal Hocko
2018-12-20 13:41 ` Oscar Salvador
2018-12-20 14:21 ` Oscar Salvador
2018-12-20 14:39 ` Michal Hocko [this message]
2018-12-20 15:37 ` Oscar Salvador
2018-12-20 15:32 ` Wei Yang
2018-12-20 15:32 ` Wei Yang
2018-12-20 15:52 ` Oscar Salvador
2018-12-20 13:08 ` Wei Yang
2018-12-20 13:49 ` Oscar Salvador
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