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 14:01:42 +0200 [thread overview]
Message-ID: <2b103abc-2921-9d8a-7280-1d6b451c34f4@redhat.com> (raw)
In-Reply-To: <5f7c4ac9-d17a-5af3-0326-1152cca38465@redhat.com>
On 06.09.21 13:50, David Hildenbrand wrote:
> 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:
Okay, I just had another look -- that won't work because as you
correctly said, it still is on the freelist ...
So your fix is certainly correct :)
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2021-09-06 12:01 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
2021-09-06 12:01 ` David Hildenbrand [this message]
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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