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SubjectRe: [PATCH] mm/page_alloc: Add a reason for reserved pages in has_unmovable_pages()
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On 10/03/2019 05:20 PM, Qian Cai wrote:
>
>
>> On Oct 3, 2019, at 7:31 AM, Anshuman Khandual <Anshuman.Khandual@arm.com> wrote:
>>
>> Ohh, never meant that the 'Reserved' bit is anything special here but it
>> is a reason to make a page unmovable unlike many other flags.
>
> But dump_page() is used everywhere, and it is better to reserve “reason” to indicate something more important rather than duplicating the page flags.
>
> Especially, it is trivial enough right now for developers look in the page flags dumping from has_unmovable_pages(), and figure out the exact branching in the code.
>

Will something like this be better ? hugepage_migration_supported() has got
uncertainty depending on platform and huge page size.

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 15c2050c629b..8dbc86696515 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8175,7 +8175,7 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
unsigned long found;
unsigned long iter = 0;
unsigned long pfn = page_to_pfn(page);
- const char *reason = "unmovable page";
+ const char *reason;

/*
* TODO we could make this much more efficient by not checking every
@@ -8194,7 +8194,7 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
if (is_migrate_cma(migratetype))
return false;

- reason = "CMA page";
+ reason = "Unmovable CMA page";
goto unmovable;
}

@@ -8206,8 +8206,10 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,

page = pfn_to_page(check);

- if (PageReserved(page))
+ if (PageReserved(page)) {
+ reason = "Unmovable reserved page";
goto unmovable;
+ }

/*
* If the zone is movable and we have ruled out all reserved
@@ -8226,8 +8228,10 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
struct page *head = compound_head(page);
unsigned int skip_pages;

- if (!hugepage_migration_supported(page_hstate(head)))
+ if (!hugepage_migration_supported(page_hstate(head))) {
+ reason = "Unmovable HugeTLB page";
goto unmovable;
+ }

skip_pages = compound_nr(head) - (page - head);
iter += skip_pages - 1;
@@ -8271,8 +8275,10 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
* is set to both of a memory hole page and a _used_ kernel
* page at boot.
*/
- if (found > count)
+ if (found > count) {
+ reason = "Unmovable non-LRU page";
goto unmovable;
+ }
}
return false;
unmovable:
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