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Message-Id: <20200903145844.2ead558f5bc3ef3d5230d30f@linux-foundation.org>
Date: Thu, 3 Sep 2020 14:58:44 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
Michal Hocko <mhocko@...e.com>,
Wei Yang <richard.weiyang@...ux.alibaba.com>,
Baoquan He <bhe@...hat.com>,
Pankaj Gupta <pankaj.gupta.linux@...il.com>,
Oscar Salvador <osalvador@...e.de>
Subject: Re: [PATCH v2 03/10] mm/memory_hotplug: simplify page offlining
On Wed, 19 Aug 2020 19:59:50 +0200 David Hildenbrand <david@...hat.com> wrote:
> We make sure that we cannot have any memory holes right at the beginning
> of offline_pages(). We no longer need walk_system_ram_range() and can
> call test_pages_isolated() and __offline_isolated_pages() directly.
>
> offlined_pages always corresponds to nr_pages, so we can simplify that.
This patch ran afoul of Pavel's "mm/memory_hotplug: drain per-cpu pages
again during memory offline", here:
> @@ -1481,7 +1459,7 @@ static int count_system_ram_pages_cb(unsigned long start_pfn,
> int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages)
> {
> const unsigned long end_pfn = start_pfn + nr_pages;
> - unsigned long pfn, system_ram_pages = 0, offlined_pages = 0;
> + unsigned long pfn, system_ram_pages = 0;
> int ret, node, nr_isolate_pageblock;
> unsigned long flags;
> struct zone *zone;
> @@ -1579,16 +1557,12 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages)
> reason = "failure to dissolve huge pages";
> goto failed_removal_isolated;
> }
> - /* check again */
> - ret = walk_system_ram_range(start_pfn, end_pfn - start_pfn,
> - NULL, check_pages_isolated_cb);
> - } while (ret);
> -
> - /* Ok, all of our target is isolated.
> - We cannot do rollback at this point. */
> - walk_system_ram_range(start_pfn, end_pfn - start_pfn,
> - &offlined_pages, offline_isolated_pages_cb);
> - pr_info("Offlined Pages %ld\n", offlined_pages);
> + } while (test_pages_isolated(start_pfn, end_pfn, MEMORY_OFFLINE));
> +
> + /* Mark all sections offline and remove free pages from the buddy. */
> + __offline_isolated_pages(start_pfn, end_pfn);
> + pr_info("Offlined Pages %ld\n", nr_pages);
> +
> /*
> * Onlining will reset pagetype flags and makes migrate type
I did this. Looks OK?
From: David Hildenbrand <david@...hat.com>
Subject: mm/memory_hotplug: simplify page offlining
We make sure that we cannot have any memory holes right at the beginning
of offline_pages(). We no longer need walk_system_ram_range() and can
call test_pages_isolated() and __offline_isolated_pages() directly.
offlined_pages always corresponds to nr_pages, so we can simplify that.
Link: https://lkml.kernel.org/r/20200819175957.28465-4-david@redhat.com
Signed-off-by: David Hildenbrand <david@...hat.com>
Acked-by: Michal Hocko <mhocko@...e.com>
Reviewed-by: Oscar Salvador <osalvador@...e.de>
Cc: Wei Yang <richard.weiyang@...ux.alibaba.com>
Cc: Baoquan He <bhe@...hat.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@...il.com>
Cc: Charan Teja Reddy <charante@...eaurora.org>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: Fenghua Yu <fenghua.yu@...el.com>
Cc: Logan Gunthorpe <logang@...tatee.com>
Cc: "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Mel Gorman <mgorman@...hsingularity.net>
Cc: Michel Lespinasse <walken@...gle.com>
Cc: Mike Rapoport <rppt@...nel.org>
Cc: Tony Luck <tony.luck@...el.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---
mm/memory_hotplug.c | 61 +++++++++++++++++-------------------------
1 file changed, 25 insertions(+), 36 deletions(-)
--- a/mm/memory_hotplug.c~mm-memory_hotplug-simplify-page-offlining
+++ a/mm/memory_hotplug.c
@@ -1383,28 +1383,6 @@ do_migrate_range(unsigned long start_pfn
return ret;
}
-/* Mark all sections offline and remove all free pages from the buddy. */
-static int
-offline_isolated_pages_cb(unsigned long start, unsigned long nr_pages,
- void *data)
-{
- unsigned long *offlined_pages = (unsigned long *)data;
-
- *offlined_pages += __offline_isolated_pages(start, start + nr_pages);
- return 0;
-}
-
-/*
- * Check all pages in range, recorded as memory resource, are isolated.
- */
-static int
-check_pages_isolated_cb(unsigned long start_pfn, unsigned long nr_pages,
- void *data)
-{
- return test_pages_isolated(start_pfn, start_pfn + nr_pages,
- MEMORY_OFFLINE);
-}
-
static int __init cmdline_parse_movable_node(char *p)
{
movable_node_enabled = true;
@@ -1491,7 +1469,7 @@ static int count_system_ram_pages_cb(uns
int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages)
{
const unsigned long end_pfn = start_pfn + nr_pages;
- unsigned long pfn, system_ram_pages = 0, offlined_pages = 0;
+ unsigned long pfn, system_ram_pages = 0;
int ret, node, nr_isolate_pageblock;
unsigned long flags;
struct zone *zone;
@@ -1589,16 +1567,27 @@ int __ref offline_pages(unsigned long st
reason = "failure to dissolve huge pages";
goto failed_removal_isolated;
}
- /* check again */
- ret = walk_system_ram_range(start_pfn, end_pfn - start_pfn,
- NULL, check_pages_isolated_cb);
- } while (ret);
-
- /* Ok, all of our target is isolated.
- We cannot do rollback at this point. */
- walk_system_ram_range(start_pfn, end_pfn - start_pfn,
- &offlined_pages, offline_isolated_pages_cb);
- pr_info("Offlined Pages %ld\n", offlined_pages);
+
+ /*
+ * per-cpu pages are drained in start_isolate_page_range, but if
+ * there are still pages that are not free, make sure that we
+ * drain again, because when we isolated range we might
+ * have raced with another thread that was adding pages to pcp
+ * list.
+ *
+ * Forward progress should be still guaranteed because
+ * pages on the pcp list can only belong to MOVABLE_ZONE
+ * because has_unmovable_pages explicitly checks for
+ * PageBuddy on freed pages on other zones.
+ */
+ if (ret)
+ drain_all_pages(zone);
+ } while (test_pages_isolated(start_pfn, end_pfn, MEMORY_OFFLINE));
+
+ /* Mark all sections offline and remove free pages from the buddy. */
+ __offline_isolated_pages(start_pfn, end_pfn);
+ pr_info("Offlined Pages %ld\n", nr_pages);
+
/*
* Onlining will reset pagetype flags and makes migrate type
* MOVABLE, so just need to decrease the number of isolated
@@ -1609,11 +1598,11 @@ int __ref offline_pages(unsigned long st
spin_unlock_irqrestore(&zone->lock, flags);
/* removal success */
- adjust_managed_page_count(pfn_to_page(start_pfn), -offlined_pages);
- zone->present_pages -= offlined_pages;
+ adjust_managed_page_count(pfn_to_page(start_pfn), -nr_pages);
+ zone->present_pages -= nr_pages;
pgdat_resize_lock(zone->zone_pgdat, &flags);
- zone->zone_pgdat->node_present_pages -= offlined_pages;
+ zone->zone_pgdat->node_present_pages -= nr_pages;
pgdat_resize_unlock(zone->zone_pgdat, &flags);
init_per_zone_wmark_min();
_
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