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Message-ID: <20181105092851.GD4361@dhcp22.suse.cz>
Date: Mon, 5 Nov 2018 10:28:51 +0100
From: Michal Hocko <mhocko@...nel.org>
To: Baoquan He <bhe@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
LKML <linux-kernel@...r.kernel.org>,
Stable tree <stable@...r.kernel.org>
Subject: Re: [PATCH] mm, memory_hotplug: teach has_unmovable_pages about of
LRU migrateable pages
On Mon 05-11-18 10:14:07, Michal Hocko wrote:
> Maybe we can add a retry for movable zone pages.
Or something like this. Ugly as hell, no question about that. I also
have to think about this some more to convince myself this will not
result in an endless loop under some situations.
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 48ceda313332..342d66eca0f3 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7779,12 +7779,16 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
pfn = page_to_pfn(page);
for (found = 0, iter = 0; iter < pageblock_nr_pages; iter++) {
unsigned long check = pfn + iter;
+ unsigned long saved_flags;
if (!pfn_valid_within(check))
continue;
page = pfn_to_page(check);
+retry:
+ saved_flags = READ_ONCE(page->flags);
+
if (PageReserved(page))
goto unmovable;
@@ -7840,6 +7844,13 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
page->mapping->a_ops->migratepage)
continue;
+ /*
+ * We might race with the allocation of the page so retry
+ * if flags have changed.
+ */
+ if (saved_flags != READ_ONCE(page->flags))
+ goto retry;
+
/*
* If there are RECLAIMABLE pages, we need to check
* it. But now, memory offline itself doesn't call
--
Michal Hocko
SUSE Labs
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