when we test the pages in a range is free or not, there is a little
chance we encounter some page which is not in buddy but page_count is 0.
That means that page could be in the page-freeing path but not in the
buddy freelist, such as in pcplist or wait for the zone->lock which the
tester is holding.
Back to the freepage_migratetype, we use it for a cached value for decide
which free-list the page go when freeing page. If the pageblock is isolated
the page will go to free-list[MIGRATE_ISOLATE] even if the cached type is
not MIGRATE_ISOLATE, the commit ad53f92e(fix incorrect isolation behavior
by rechecking migratetype) patch series have ensure this.
So the freepage_migratetype check for page_count==0 page in
__test_page_isolated_in_pageblock() is meaningless.
This patch removes the unnecessary freepage_migratetype check.
Signed-off-by: Weijie Yang <[email protected]>
---
mm/page_isolation.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index 6e5174d..f7c9183 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -223,8 +223,7 @@ __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn,
page = pfn_to_page(pfn);
if (PageBuddy(page))
pfn += 1 << page_order(page);
- else if (page_count(page) == 0 &&
- get_freepage_migratetype(page) == MIGRATE_ISOLATE)
+ else if (page_count(page) == 0)
pfn += 1;
else if (skip_hwpoisoned_pages && PageHWPoison(page)) {
/*
--
1.7.10.4
On 12/09/2014 08:51 AM, Weijie Yang wrote:
> when we test the pages in a range is free or not, there is a little
> chance we encounter some page which is not in buddy but page_count is 0.
> That means that page could be in the page-freeing path but not in the
> buddy freelist, such as in pcplist
This shouldn't happen anymore IMHO. The pageblock is marked as
MIGRATE_ISOLATE and then a lru+pcplist drain is performed. Nothing
should be left on pcplist - anything newly freed goes directly to free
lists. Hm, maybe it could be on lru cache, but that holds a page
reference IIRC, so this test won't pass.
> or wait for the zone->lock which the
> tester is holding.
That could maybe happen, but is it worth testing? If yes, please add it
in a comment to the code.
> Back to the freepage_migratetype, we use it for a cached value for decide
> which free-list the page go when freeing page. If the pageblock is isolated
> the page will go to free-list[MIGRATE_ISOLATE] even if the cached type is
> not MIGRATE_ISOLATE, the commit ad53f92e(fix incorrect isolation behavior
> by rechecking migratetype) patch series have ensure this.
>
> So the freepage_migratetype check for page_count==0 page in
> __test_page_isolated_in_pageblock() is meaningless.
> This patch removes the unnecessary freepage_migratetype check.
>
> Signed-off-by: Weijie Yang <[email protected]>
> ---
> mm/page_isolation.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index 6e5174d..f7c9183 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -223,8 +223,7 @@ __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn,
> page = pfn_to_page(pfn);
> if (PageBuddy(page))
> pfn += 1 << page_order(page);
> - else if (page_count(page) == 0 &&
> - get_freepage_migratetype(page) == MIGRATE_ISOLATE)
> + else if (page_count(page) == 0)
> pfn += 1;
> else if (skip_hwpoisoned_pages && PageHWPoison(page)) {
> /*
>
On Tue, Dec 9, 2014 at 5:24 PM, Vlastimil Babka <[email protected]> wrote:
> On 12/09/2014 08:51 AM, Weijie Yang wrote:
>>
>> when we test the pages in a range is free or not, there is a little
>> chance we encounter some page which is not in buddy but page_count is 0.
>> That means that page could be in the page-freeing path but not in the
>> buddy freelist, such as in pcplist
>
>
> This shouldn't happen anymore IMHO. The pageblock is marked as
> MIGRATE_ISOLATE and then a lru+pcplist drain is performed. Nothing should be
> left on pcplist - anything newly freed goes directly to free lists. Hm,
> maybe it could be on lru cache, but that holds a page reference IIRC, so
> this test won't pass.
Yes, you are right. I made a mistake, this shouldn't happen.
I will remove this description in next version. Thanks.
>> or wait for the zone->lock which the
>> tester is holding.
>
>
> That could maybe happen, but is it worth testing? If yes, please add it in a
> comment to the code.
This could happen even though the chance is very tiny.
As for cma_alloc, the test makes no difference.
However, as for offline_page, the test makes sense. If we leave the test and
pass it when page_count is zero, it could trigger the BUG_ON(!PageBuddy(page))
in the __offline_isolated_pages() if the page hasn't finish its free journey.
>From the literal meaning of this test_pages_isolated() function, I think it is
better get a definite result and not leave some middle status even if
they are rare.
So, Let's remove the whole test branch
(page_count(page) == 0 && get_freepage_migratetype(page) == MIGRATE_ISOLATE)
Thanks for your remind and suggestion.
>
>> Back to the freepage_migratetype, we use it for a cached value for decide
>> which free-list the page go when freeing page. If the pageblock is
>> isolated
>> the page will go to free-list[MIGRATE_ISOLATE] even if the cached type is
>> not MIGRATE_ISOLATE, the commit ad53f92e(fix incorrect isolation behavior
>> by rechecking migratetype) patch series have ensure this.
>>
>> So the freepage_migratetype check for page_count==0 page in
>> __test_page_isolated_in_pageblock() is meaningless.
>> This patch removes the unnecessary freepage_migratetype check.
>>
>> Signed-off-by: Weijie Yang <[email protected]>
>> ---
>> mm/page_isolation.c | 3 +--
>> 1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
>> index 6e5174d..f7c9183 100644
>> --- a/mm/page_isolation.c
>> +++ b/mm/page_isolation.c
>> @@ -223,8 +223,7 @@ __test_page_isolated_in_pageblock(unsigned long pfn,
>> unsigned long end_pfn,
>> page = pfn_to_page(pfn);
>> if (PageBuddy(page))
>> pfn += 1 << page_order(page);
>> - else if (page_count(page) == 0 &&
>> - get_freepage_migratetype(page) == MIGRATE_ISOLATE)
>> + else if (page_count(page) == 0)
>> pfn += 1;
>> else if (skip_hwpoisoned_pages && PageHWPoison(page)) {
>> /*
>>
>