Re: [PATCH V3 1/2] mm: hotplug: implement non-movable version ofget_user_pages() called get_user_pages_non_movable()

[Lin Feng]

Hi Andrew, Mel and other guys,

How about this V3 patch, any comments?

thanks,
linfeng

On 02/21/2013 07:01 PM, Lin Feng wrote:
> get_user_pages() always tries to allocate pages from movable zone, which is not
>  reliable to memory hotremove framework in some case.
> 
> This patch introduces a new library function called get_user_pages_non_movable()
>  to pin pages only from zone non-movable in memory.
> It's a wrapper of get_user_pages() but it makes sure that all pages come from
> non-movable zone via additional page migration. But if migration fails it
> will at least keep the base functionality of get_user_pages().
> 
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> Cc: Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx>
> Cc: Jeff Moyer <jmoyer@xxxxxxxxxx>
> Cc: Minchan Kim <minchan@xxxxxxxxxx>
> Cc: Zach Brown <zab@xxxxxxxxxx>
> Reviewed-by: Tang Chen <tangchen@xxxxxxxxxxxxxx>
> Reviewed-by: Gu Zheng <guz.fnst@xxxxxxxxxxxxxx>
> Signed-off-by: Lin Feng <linfeng@xxxxxxxxxxxxxx>
> ---
>  include/linux/mm.h     |   14 ++++++
>  include/linux/mmzone.h |    4 ++
>  mm/memory.c            |  103 ++++++++++++++++++++++++++++++++++++++++++++++++
>  mm/page_isolation.c    |    8 ++++
>  4 files changed, 129 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 5625c1c..737dc39 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1025,6 +1025,20 @@ long get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
>  		    struct vm_area_struct **vmas);
>  int get_user_pages_fast(unsigned long start, int nr_pages, int write,
>  			struct page **pages);
> +#ifdef CONFIG_MEMORY_HOTREMOVE
> +int get_user_pages_non_movable(struct task_struct *tsk, struct mm_struct *mm,
> +		unsigned long start, int nr_pages, int write, int force,
> +		struct page **pages, struct vm_area_struct **vmas);
> +#else
> +static inline
> +int get_user_pages_non_movable(struct task_struct *tsk, struct mm_struct *mm,
> +		unsigned long start, int nr_pages, int write, int force,
> +		struct page **pages, struct vm_area_struct **vmas)
> +{
> +	return get_user_pages(tsk, mm, start, nr_pages, write, force, pages,
> +				vmas);
> +}
> +#endif
>  struct kvec;
>  int get_kernel_pages(const struct kvec *iov, int nr_pages, int write,
>  			struct page **pages);
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index ab20a60..c31007e 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -851,6 +851,10 @@ static inline int is_normal_idx(enum zone_type idx)
>  	return (idx == ZONE_NORMAL);
>  }
>  
> +static inline int zone_is_movable(struct zone *zone)
> +{
> +	return zone_idx(zone) == ZONE_MOVABLE;
> +}
>  /**
>   * is_highmem - helper function to quickly check if a struct zone is a 
>   *              highmem zone or not.  This is an attempt to keep references
> diff --git a/mm/memory.c b/mm/memory.c
> index 16ca5d0..83db7dd 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -58,6 +58,8 @@
>  #include <linux/elf.h>
>  #include <linux/gfp.h>
>  #include <linux/migrate.h>
> +#include <linux/page-isolation.h>
> +#include <linux/mm_inline.h>
>  #include <linux/string.h>
>  
>  #include <asm/io.h>
> @@ -2014,6 +2016,107 @@ long get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
>  }
>  EXPORT_SYMBOL(get_user_pages);
>  
> +#ifdef CONFIG_MEMORY_HOTREMOVE
> +/**
> + * It's a wrapper of get_user_pages() but it makes sure that all pages come from
> + * non-movable zone via additional page migration. It's designed for memory
> + * hotremove framework.
> + *
> + * Currently get_user_pages() always tries to allocate pages from movable zone,
> + * in some case users of get_user_pages() is easy to pin user pages for a long
> + * time(for now we found that pages pinned as aio ring pages is such case),
> + * which is fatal for memory hotremove framework.
> + *
> + * This function first calls get_user_pages() to get the candidate pages, and
> + * then check to ensure all pages are from non movable zone. Otherwise migrate
> + * them to non movable zone, then retry. It will at most retry once. If
> + * migration fails, it will keep the base functionality of get_user_pages()
> + * and issue WARN message for memory hot-remove people.
> + *
> + * Fixme: now we don't support non movable version of GUP for hugepage.
> + */
> +int get_user_pages_non_movable(struct task_struct *tsk, struct mm_struct *mm,
> +		unsigned long start, int nr_pages, int write, int force,
> +		struct page **pages, struct vm_area_struct **vmas)
> +{
> +	int ret, i, tried = 0;
> +	bool isolate_err, migrate_prepped;
> +	LIST_HEAD(pagelist);
> +
> +retry:
> +	BUG_ON(tried == 2);
> +	ret = get_user_pages(tsk, mm, start, nr_pages, write, force, pages,
> +				vmas);
> +	/* No ZONE_MOVABLE populated, all pages are from non movable zone */
> +	if (movable_zone == ZONE_MOVABLE || ret <= 0)
> +		return ret;
> +
> +	isolate_err = false;
> +	migrate_prepped = false;
> +
> +	for (i = 0; i < ret; i++) {
> +		if (zone_is_movable(page_zone(pages[i]))) {
> +			/* Fixme: improve for hugepage non movable support */
> +			if (PageHuge(pages[i])) {
> +				WARN_ONCE(1, "Non movable GUP for hugepages "
> +					"haven't been implemented yet, it may "
> +					"lead to memory hot-remove failure.\n");
> +				continue;
> +			}
> +
> +			/* Hugepage or THP's head page has covered tail pages */
> +			if (PageTail(pages[i]) && (page_count(pages[i]) == 1))
> +				continue;
> +
> +			if (!migrate_prepped) {
> +				BUG_ON(migrate_prep());
> +				migrate_prepped = true;
> +			}
> +
> +			/* Fixme: isolate_lru_page() takes the LRU lock every
> +			 * time, batching the lock could avoid potential lock
> +			 * contention problems. -Mel Gorman
> +			 */
> +			if (!isolate_lru_page(pages[i])) {
> +				inc_zone_page_state(pages[i], NR_ISOLATED_ANON +
> +						 page_is_file_cache(pages[i]));
> +				list_add(&pages[i]->lru, &pagelist);
> +			} else {
> +				isolate_err = true;
> +				break;
> +			}
> +		}
> +	}
> +
> +	/* All pages are non movable, we are done :) */
> +	if (i == ret && list_empty(&pagelist))
> +		return ret;
> +
> +	/* Undo the effects of former get_user_pages(), ready for another try */
> +	release_pages(pages, ret, 1);
> +
> +	if (!isolate_err) {
> +		ret = migrate_pages(&pagelist, alloc_migrate_target, 1,
> +					MIGRATE_SYNC, MR_SYSCALL);
> +		/* Steal pages from non-movable zone successfully? */
> +		if (!ret) {
> +			tried++;
> +			goto retry;
> +		}
> +	}
> +
> +	putback_lru_pages(&pagelist);
> +	/* Migration failed, in order to keep at least the base functionality of
> +	 * get_user_pages(), we pin pages again but give WARN info to remind
> +	 * memory hot-remove people, which is a trade-off.
> +	 */
> +	WARN_ONCE(1, "Non movable zone migration failed, "
> +		"it may lead to memroy hot-remove failure.\n");
> +	return get_user_pages(tsk, mm, start, nr_pages, write, force, pages,
> +				vmas);
> +}
> +EXPORT_SYMBOL(get_user_pages_non_movable);
> +#endif
>  /**
>   * get_dump_page() - pin user page in memory while writing it to core dump
>   * @addr: user address
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index 383bdbb..7823ea5 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -247,6 +247,9 @@ int test_pages_isolated(unsigned long start_pfn, unsigned long end_pfn,
>  	return ret ? 0 : -EBUSY;
>  }
>  
> +/**
> + * @private: 0 means page can be alloced from movable zone, otherwise forbidden
> + */
>  struct page *alloc_migrate_target(struct page *page, unsigned long private,
>  				  int **resultp)
>  {
> @@ -254,6 +257,11 @@ struct page *alloc_migrate_target(struct page *page, unsigned long private,
>  
>  	if (PageHighMem(page))
>  		gfp_mask |= __GFP_HIGHMEM;
> +#if defined(CONFIG_MEMORY_HOTREMOVE) && defined(CONFIG_HIGHMEM)
> +	BUILD_BUG_ON(1);
> +#endif
> +	if (unlikely(private != 0))
> +		gfp_mask &= ~__GFP_HIGHMEM;
>  
>  	return alloc_page(gfp_mask);
>  }
> 
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