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SubjectRe: [RFC/PATCH 4/5] mm: get_user_pages: migrate out CMA pages when FOLL_DURABLE flag is set
2013/03/05 15:57, Marek Szyprowski wrote:
> When __get_user_pages() is called with FOLL_DURABLE flag, ensure that no
> page in CMA pageblocks gets locked. This workarounds the permanent
> migration failures caused by locking the pages by get_user_pages() call for
> a long period of time.
>
> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
> ---
> mm/internal.h | 12 ++++++++++++
> mm/memory.c | 43 +++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 55 insertions(+)
>
> diff --git a/mm/internal.h b/mm/internal.h
> index 8562de0..a290d04 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -105,6 +105,18 @@ extern void prep_compound_page(struct page *page, unsigned long order);
> extern bool is_free_buddy_page(struct page *page);
> #endif
>
> +#ifdef CONFIG_CMA
> +static inline int is_cma_page(struct page *page)
> +{
> + unsigned mt = get_pageblock_migratetype(page);
> + if (mt == MIGRATE_ISOLATE || mt == MIGRATE_CMA)
> + return true;
> + return false;
> +}
> +#else
> +#define is_cma_page(page) 0
> +#endif
> +
> #if defined CONFIG_COMPACTION || defined CONFIG_CMA
>
> /*
> diff --git a/mm/memory.c b/mm/memory.c
> index 2b9c2dd..f81b273 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1650,6 +1650,45 @@ static inline int stack_guard_page(struct vm_area_struct *vma, unsigned long add
> }
>
> /**
> + * replace_cma_page() - migrate page out of CMA page blocks
> + * @page: source page to be migrated
> + *
> + * Returns either the old page (if migration was not possible) or the pointer
> + * to the newly allocated page (with additional reference taken).
> + *
> + * get_user_pages() might take a reference to a page for a long period of time,
> + * what prevent such page from migration. This is fatal to the preffered usage
> + * pattern of CMA pageblocks. This function replaces the given user page with
> + * a new one allocated from NON-MOVABLE pageblock, so locking CMA page can be
> + * avoided.
> + */
> +static inline struct page *migrate_replace_cma_page(struct page *page)
> +{
> + struct page *newpage = alloc_page(GFP_HIGHUSER);
> +
> + if (!newpage)
> + goto out;
> +
> + /*
> + * Take additional reference to the new page to ensure it won't get
> + * freed after migration procedure end.
> + */
> + get_page_foll(newpage);
> +
> + if (migrate_replace_page(page, newpage) == 0)
> + return newpage;
> +
> + put_page(newpage);
> + __free_page(newpage);
> +out:
> + /*
> + * Migration errors in case of get_user_pages() might not
> + * be fatal to CMA itself, so better don't fail here.
> + */
> + return page;
> +}
> +
> +/**
> * __get_user_pages() - pin user pages in memory
> * @tsk: task_struct of target task
> * @mm: mm_struct of target mm
> @@ -1884,6 +1923,10 @@ long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
> }
> if (IS_ERR(page))
> return i ? i : PTR_ERR(page);

> +
> + if ((gup_flags & FOLL_DURABLE) && is_cma_page(page))
> + page = migrate_replace_cma_page(page);
> +

I might be misreading.
If FOLL_DURABLE is set, this page is always allocated as non movable.
Is it right? If so, when does this situation occur?

Thanks,
Yasuaki Ishimatsu

> if (pages) {
> pages[i] = page;
>
>




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