From: Mel Gorman <mgorman@suse.de>
To: Andrea Arcangeli <aarcange@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, Qian Cai <cai@lca.pw>,
Michal Hocko <mhocko@kernel.org>,
David Hildenbrand <david@redhat.com>,
linux-kernel@vger.kernel.org, Mike Rapoport <rppt@linux.ibm.com>,
Baoquan He <bhe@redhat.com>
Subject: Re: [PATCH 1/1] mm: compaction: avoid fast_isolate_around() to set pageblock_skip on reserved pages
Date: Sun, 6 Dec 2020 23:47:26 +0000 [thread overview]
Message-ID: <20201206234726.GH3306@suse.de> (raw)
In-Reply-To: <X8xBZ03epeQD/hsn@redhat.com>
On Sat, Dec 05, 2020 at 09:26:47PM -0500, Andrea Arcangeli wrote:
> Hi Mel,
>
> On Thu, Nov 26, 2020 at 10:47:20AM +0000, Mel Gorman wrote:
> > Agreed. This thread has a lot of different directions in it at this
> > point so what I'd hope for is first, a patch that initialises holes with
> > zone/node linkages within a 1<<(MAX_ORDER-1) alignment. If there is a
> > hole, it would be expected the pages are PageReserved. Second, a fix to
> > fast_isolate that forces PFNs returned to always be within the stated
> > zone boundaries.
>
> The last two patches should resolve the struct page
> initialization
> https://git.kernel.org/pub/scm/linux/kernel/git/andrea/aa.git/ and the
> VM_BUG_ON_PAGE never happened again as expected.
>
> So I looked back to see how the "distance" logic is accurate. I added
> those checks and I get negative hits:
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index cc1a7f600a86..844a90b0acdf 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1331,6 +1331,12 @@ fast_isolate_freepages(struct compact_control *cc)
> low_pfn = pageblock_start_pfn(cc->free_pfn - (distance >> 2));
> min_pfn = pageblock_start_pfn(cc->free_pfn - (distance >> 1));
>
> + WARN_ON_ONCE((long) low_pfn < 0);
> + WARN_ON_ONCE((long) min_pfn < 0);
> + if ((long) low_pfn < 0)
> + return cc->free_pfn;
> + if ((long) min_pfn < 0)
> + return cc->free_pfn;
> if (WARN_ON_ONCE(min_pfn > low_pfn))
> low_pfn = min_pfn;
>
> Both warn-on-once triggers, so it goes negative. While it appears not
> kernel crashing since pfn_valid won't succeed on negative entries and
> they'll always be higher than any pfn in the freelist, is this sign
> that there's further room for improvement here?
>
Possibly, checking the wrong pfns is simply risky. This is not tested
at all, just checking if it's in the right ballpark even. Intent is that
when the free/migrate PFNs are too close or already overlapping that no
attempt is made and it returns back to detect the scanners have met.
diff --git a/mm/compaction.c b/mm/compaction.c
index 13cb7a961b31..208cb5857446 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1313,6 +1313,10 @@ fast_isolate_freepages(struct compact_control *cc)
if (cc->order <= 0)
return cc->free_pfn;
+ /* Ensure that migration and free scanner are not about to cross */
+ if (cc->migrate_pfn < cc->free_pfn)
+ return cc->free_pfn;
+
/*
* If starting the scan, use a deeper search and use the highest
* PFN found if a suitable one is not found.
@@ -1324,9 +1328,12 @@ fast_isolate_freepages(struct compact_control *cc)
/*
* Preferred point is in the top quarter of the scan space but take
- * a pfn from the top half if the search is problematic.
+ * a pfn from the top half if the search is problematic. Ensure
+ * there is enough distance to make the fast search worthwhile.
*/
distance = (cc->free_pfn - cc->migrate_pfn);
+ if (distance <= (pageblock_nr_pages << 2))
+ return cc->free_pfn;
low_pfn = pageblock_start_pfn(cc->free_pfn - (distance >> 2));
min_pfn = pageblock_start_pfn(cc->free_pfn - (distance >> 1));
--
Mel Gorman
SUSE Labs
next prev parent reply other threads:[~2020-12-06 23:48 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-23 21:25 compaction: VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn)) Qian Cai
2020-04-24 3:43 ` Baoquan He
2020-04-24 13:45 ` Qian Cai
2020-05-05 12:43 ` Baoquan He
2020-05-05 13:20 ` Qian Cai
2020-05-11 1:21 ` Baoquan He
2020-04-26 14:41 ` Mike Rapoport
2020-04-27 13:45 ` Qian Cai
2020-11-21 19:45 ` [PATCH 0/1] VM_BUG_ON_PAGE(!zone_spans_pfn) in set_pfnblock_flags_mask Andrea Arcangeli
2020-11-21 19:45 ` [PATCH 1/1] mm: compaction: avoid fast_isolate_around() to set pageblock_skip on reserved pages Andrea Arcangeli
2020-11-21 19:53 ` Andrea Arcangeli
2020-11-23 11:26 ` David Hildenbrand
2020-11-23 13:01 ` Vlastimil Babka
2020-11-24 13:32 ` Mel Gorman
2020-11-24 20:56 ` Andrea Arcangeli
2020-11-25 10:30 ` Mel Gorman
2020-11-25 17:59 ` Andrea Arcangeli
2020-11-26 10:47 ` Mel Gorman
2020-12-06 2:26 ` Andrea Arcangeli
2020-12-06 23:47 ` Mel Gorman [this message]
2020-11-25 5:34 ` Andrea Arcangeli
2020-11-25 6:45 ` David Hildenbrand
2020-11-25 8:51 ` Mike Rapoport
2020-11-25 10:39 ` Mel Gorman
2020-11-25 11:04 ` David Hildenbrand
2020-11-25 11:41 ` David Hildenbrand
2020-11-25 18:47 ` Andrea Arcangeli
2020-11-25 13:33 ` Mel Gorman
2020-11-25 13:41 ` David Hildenbrand
2020-11-25 18:28 ` Andrea Arcangeli
2020-11-25 19:27 ` David Hildenbrand
2020-11-25 20:41 ` Andrea Arcangeli
2020-11-25 21:13 ` David Hildenbrand
2020-11-25 21:04 ` Mike Rapoport
2020-11-25 21:38 ` Andrea Arcangeli
2020-11-26 9:36 ` Mike Rapoport
2020-11-26 10:05 ` David Hildenbrand
2020-11-26 17:46 ` Mike Rapoport
2020-11-29 12:32 ` Mike Rapoport
2020-12-02 0:44 ` Andrea Arcangeli
2020-12-02 17:39 ` Mike Rapoport
2020-12-03 6:23 ` Andrea Arcangeli
2020-12-03 10:51 ` Mike Rapoport
2020-12-03 17:31 ` Andrea Arcangeli
2020-12-06 8:09 ` Mike Rapoport
2020-11-26 18:15 ` Andrea Arcangeli
2020-11-26 18:29 ` Andrea Arcangeli
2020-11-26 19:44 ` Mike Rapoport
2020-11-26 20:30 ` Andrea Arcangeli
2020-11-26 21:03 ` Mike Rapoport
2020-11-26 19:21 ` Andrea Arcangeli
2020-11-25 12:08 ` Vlastimil Babka
2020-11-25 13:32 ` David Hildenbrand
2020-11-25 14:13 ` Mike Rapoport
2020-11-25 14:42 ` David Hildenbrand
2020-11-26 10:51 ` Mel Gorman
2020-11-25 19:14 ` Andrea Arcangeli
2020-11-25 19:01 ` Andrea Arcangeli
2020-11-25 19:33 ` David Hildenbrand
2020-11-26 3:40 ` Andrea Arcangeli
2020-11-26 10:43 ` Mike Rapoport
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