Re: [PATCH 2/5] vrange: Add purged page detection on setting memory non-volatile

[Jan Kara <jack@suse.cz>]

On Fri 21-03-14 14:17:32, John Stultz wrote:
> Users of volatile ranges will need to know if memory was discarded.
> This patch adds the purged state tracking required to inform userland
> when it marks memory as non-volatile that some memory in that range
> was purged and needs to be regenerated.
> 
> This simplified implementation which uses some of the logic from
> Minchan's earlier efforts, so credit to Minchan for his work.
> 
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Android Kernel Team <kernel-team@android.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Robert Love <rlove@google.com>
> Cc: Mel Gorman <mel@csn.ul.ie>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Dave Hansen <dave@sr71.net>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: Dmitry Adamushko <dmitry.adamushko@gmail.com>
> Cc: Neil Brown <neilb@suse.de>
> Cc: Andrea Arcangeli <aarcange@redhat.com>
> Cc: Mike Hommey <mh@glandium.org>
> Cc: Taras Glek <tglek@mozilla.com>
> Cc: Jan Kara <jack@suse.cz>
> Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
> Cc: Michel Lespinasse <walken@google.com>
> Cc: Minchan Kim <minchan@kernel.org>
> Cc: linux-mm@kvack.org <linux-mm@kvack.org>
> Signed-off-by: John Stultz <john.stultz@linaro.org>
  Just one minor nit below. Otherwise the patch looks good to me. So you
can add
Acked-by: Jan Kara <jack@suse.cz>

								Honza

> ---
>  include/linux/swap.h    | 15 ++++++++--
>  include/linux/swapops.h | 10 +++++++
>  include/linux/vrange.h  |  3 ++
>  mm/vrange.c             | 75 +++++++++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 101 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 46ba0c6..18c12f9 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -70,8 +70,19 @@ static inline int current_is_kswapd(void)
>  #define SWP_HWPOISON_NUM 0
>  #endif
>  
> -#define MAX_SWAPFILES \
> -	((1 << MAX_SWAPFILES_SHIFT) - SWP_MIGRATION_NUM - SWP_HWPOISON_NUM)
> +
> +/*
> + * Purged volatile range pages
> + */
> +#define SWP_VRANGE_PURGED_NUM 1
> +#define SWP_VRANGE_PURGED (MAX_SWAPFILES + SWP_HWPOISON_NUM + SWP_MIGRATION_NUM)
> +
> +
> +#define MAX_SWAPFILES ((1 << MAX_SWAPFILES_SHIFT)	\
> +				- SWP_MIGRATION_NUM	\
> +				- SWP_HWPOISON_NUM	\
> +				- SWP_VRANGE_PURGED_NUM	\
> +			)
>  
>  /*
>   * Magic header for a swap area. The first part of the union is
> diff --git a/include/linux/swapops.h b/include/linux/swapops.h
> index c0f7526..84f43d9 100644
> --- a/include/linux/swapops.h
> +++ b/include/linux/swapops.h
> @@ -161,6 +161,16 @@ static inline int is_write_migration_entry(swp_entry_t entry)
>  
>  #endif
>  
> +static inline swp_entry_t make_vpurged_entry(void)
> +{
> +	return swp_entry(SWP_VRANGE_PURGED, 0);
> +}
> +
> +static inline int is_vpurged_entry(swp_entry_t entry)
> +{
> +	return swp_type(entry) == SWP_VRANGE_PURGED;
> +}
> +
>  #ifdef CONFIG_MEMORY_FAILURE
>  /*
>   * Support for hardware poisoned pages
> diff --git a/include/linux/vrange.h b/include/linux/vrange.h
> index 6e5331e..986fa85 100644
> --- a/include/linux/vrange.h
> +++ b/include/linux/vrange.h
> @@ -1,6 +1,9 @@
>  #ifndef _LINUX_VRANGE_H
>  #define _LINUX_VRANGE_H
>  
> +#include <linux/swap.h>
> +#include <linux/swapops.h>
> +
>  #define VRANGE_NONVOLATILE 0
>  #define VRANGE_VOLATILE 1
>  #define VRANGE_VALID_FLAGS (0) /* Don't yet support any flags */
> diff --git a/mm/vrange.c b/mm/vrange.c
> index 2f8e2ce..1ff3cbd 100644
> --- a/mm/vrange.c
> +++ b/mm/vrange.c
> @@ -8,6 +8,76 @@
>  #include <linux/mm_inline.h>
>  #include "internal.h"
>  
> +struct vrange_walker {
> +	struct vm_area_struct *vma;
> +	int page_was_purged;
> +};
> +
> +
> +/**
> + * vrange_check_purged_pte - Checks ptes for purged pages
> + *
> + * Iterates over the ptes in the pmd checking if they have
> + * purged swap entries.
> + *
> + * Sets the vrange_walker.pages_purged to 1 if any were purged.
                              ^^^ page_was_purged

> + */
> +static int vrange_check_purged_pte(pmd_t *pmd, unsigned long addr,
> +					unsigned long end, struct mm_walk *walk)
> +{
> +	struct vrange_walker *vw = walk->private;
> +	pte_t *pte;
> +	spinlock_t *ptl;
> +
> +	if (pmd_trans_huge(*pmd))
> +		return 0;
> +	if (pmd_trans_unstable(pmd))
> +		return 0;
> +
> +	pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
> +	for (; addr != end; pte++, addr += PAGE_SIZE) {
> +		if (!pte_present(*pte)) {
> +			swp_entry_t vrange_entry = pte_to_swp_entry(*pte);
> +
> +			if (unlikely(is_vpurged_entry(vrange_entry))) {
> +				vw->page_was_purged = 1;
> +				break;
> +			}
> +		}
> +	}
> +	pte_unmap_unlock(pte - 1, ptl);
> +	cond_resched();
> +
> +	return 0;
> +}
> +
> +
> +/**
> + * vrange_check_purged - Sets up a mm_walk to check for purged pages
> + *
> + * Sets up and calls wa_page_range() to check for purge pages.
> + *
> + * Returns 1 if pages in the range were purged, 0 otherwise.
> + */
> +static int vrange_check_purged(struct mm_struct *mm,
> +					 struct vm_area_struct *vma,
> +					 unsigned long start,
> +					 unsigned long end)
> +{
> +	struct vrange_walker vw;
> +	struct mm_walk vrange_walk = {
> +		.pmd_entry = vrange_check_purged_pte,
> +		.mm = vma->vm_mm,
> +		.private = &vw,
> +	};
> +	vw.page_was_purged = 0;
> +	vw.vma = vma;
> +
> +	walk_page_range(start, end, &vrange_walk);
> +
> +	return vw.page_was_purged;
> +
> +}
>  
>  /**
>   * do_vrange - Marks or clears VMAs in the range (start-end) as VM_VOLATILE
> @@ -106,6 +176,11 @@ success:
>  		vma = prev->vm_next;
>  	}
>  out:
> +	if (count && (mode == VRANGE_NONVOLATILE))
> +		*purged = vrange_check_purged(mm, vma,
> +						orig_start,
> +						orig_start+count);
> +
>  	up_read(&mm->mmap_sem);
>  
>  	/* report bytes successfully marked, even if we're exiting on error */
> -- 
> 1.8.3.2
> 
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR