From: David Hildenbrand <david@redhat.com>
To: Miaohe Lin <linmiaohe@huawei.com>, akpm@linux-foundation.org
Cc: vbabka@suse.cz, iamjoonsoo.kim@lge.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/page_isolation: don't putback unisolated page
Date: Mon, 6 Sep 2021 13:50:10 +0200 [thread overview]
Message-ID: <5f7c4ac9-d17a-5af3-0326-1152cca38465@redhat.com> (raw)
In-Reply-To: <b533742e-e82a-a721-9a24-4087688dd812@huawei.com>
On 06.09.21 13:32, Miaohe Lin wrote:
> On 2021/9/6 17:40, David Hildenbrand wrote:
>> On 04.09.21 11:18, Miaohe Lin wrote:
>>> If __isolate_free_page() failed, due to zone watermark check, the page is
>>> still on the free list. But this page will be put back to free list again
>>> via __putback_isolated_page() now. This may trigger page->flags checks in
>>> __free_one_page() if PageReported is set. Or we will corrupt the free list
>>> because list_add() will be called for pages already on another list.
>>>
>>> Fixes: 3c605096d315 ("mm/page_alloc: restrict max order of merging on isolated pageblock")
>>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
>>> ---
>>> mm/page_isolation.c | 6 ++----
>>> 1 file changed, 2 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
>>> index 9bb562d5d194..7d70d772525c 100644
>>> --- a/mm/page_isolation.c
>>> +++ b/mm/page_isolation.c
>>> @@ -93,10 +93,8 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
>>> buddy_pfn = __find_buddy_pfn(pfn, order);
>>> buddy = page + (buddy_pfn - pfn);
>>> - if (!is_migrate_isolate_page(buddy)) {
>>> - __isolate_free_page(page, order);
>>> - isolated_page = true;
>>> - }
>>> + if (!is_migrate_isolate_page(buddy))
>>> + isolated_page = !!__isolate_free_page(page, order);
>>> }
>>> }
>>>
>>
>> Shouldn't we much rather force to ignore watermarks here and make sure __isolate_free_page() never fails?
>
> It seems it is not easy to force to ignore watermarks here. And it's not a problem
> if __isolate_free_page() fails because we can do move_freepages_block() anyway.
> What do you think? Many thanks.
I'm wondering if all this complexity in this function is even required. What about something like this: (completely untested)
diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index bddf788f45bf..29ff2fcb339c 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -66,12 +66,10 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_
static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
{
+ bool buddy_merge_possible = false;
struct zone *zone;
unsigned long flags, nr_pages;
- bool isolated_page = false;
unsigned int order;
- unsigned long pfn, buddy_pfn;
- struct page *buddy;
zone = page_zone(page);
spin_lock_irqsave(&zone->lock, flags);
@@ -79,26 +77,15 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
goto out;
/*
- * Because freepage with more than pageblock_order on isolated
- * pageblock is restricted to merge due to freepage counting problem,
- * it is possible that there is free buddy page.
- * move_freepages_block() doesn't care of merge so we need other
- * approach in order to merge them. Isolation and free will make
- * these pages to be merged.
+ * If our free page spans at least this whole pageblock and could
+ * eventually get merged into an even bigger page, go via
+ * __putback_isolated_page(), because move_freepages_block() won't
+ * trigger merging of free pages.
*/
if (PageBuddy(page)) {
order = buddy_order(page);
- if (order >= pageblock_order && order < MAX_ORDER - 1) {
- pfn = page_to_pfn(page);
- buddy_pfn = __find_buddy_pfn(pfn, order);
- buddy = page + (buddy_pfn - pfn);
-
- if (pfn_valid_within(buddy_pfn) &&
- !is_migrate_isolate_page(buddy)) {
- __isolate_free_page(page, order);
- isolated_page = true;
- }
- }
+ if (order >= pageblock_order && order < MAX_ORDER - 1)
+ buddy_merge_possible = true;
}
/*
@@ -111,12 +98,12 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
* onlining - just onlined memory won't immediately be considered for
* allocation.
*/
- if (!isolated_page) {
+ if (!buddy_merge_possible) {
nr_pages = move_freepages_block(zone, page, migratetype, NULL);
__mod_zone_freepage_state(zone, nr_pages, migratetype);
}
set_pageblock_migratetype(page, migratetype);
- if (isolated_page)
+ if (buddy_merge_possible)
__putback_isolated_page(page, order, migratetype);
zone->nr_isolate_pageblock--;
out:
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2021-09-06 11:50 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-04 9:18 [PATCH] mm/page_isolation: don't putback unisolated page Miaohe Lin
2021-09-06 9:40 ` David Hildenbrand
2021-09-06 11:32 ` Miaohe Lin
2021-09-06 11:50 ` David Hildenbrand [this message]
2021-09-06 12:01 ` David Hildenbrand
2021-09-06 12:08 ` Miaohe Lin
2021-09-06 12:02 ` David Hildenbrand
2021-09-06 12:11 ` David Hildenbrand
2021-09-06 12:45 ` Miaohe Lin
2021-09-06 12:49 ` David Hildenbrand
2021-09-07 1:46 ` Miaohe Lin
2021-09-07 9:52 ` David Hildenbrand
2021-09-07 8:08 ` Vlastimil Babka
2021-09-07 9:56 ` David Hildenbrand
2021-09-08 22:42 ` John Hubbard
2021-09-09 8:56 ` David Hildenbrand
2021-09-09 9:07 ` Vlastimil Babka
2021-09-09 9:37 ` David Hildenbrand
2021-09-09 16:50 ` John Hubbard
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