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

From: Jan Kara
Date: Sun Mar 23 2014 - 10:10:07 EST

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@xxxxxxxxxxxxxxxxxxxx>
> Cc: Android Kernel Team <kernel-team@xxxxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Robert Love <rlove@xxxxxxxxxx>
> Cc: Mel Gorman <mel@xxxxxxxxx>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: Dave Hansen <dave@xxxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxx>
> Cc: Dmitry Adamushko <dmitry.adamushko@xxxxxxxxx>
> Cc: Neil Brown <neilb@xxxxxxx>
> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Cc: Mike Hommey <mh@xxxxxxxxxxxx>
> Cc: Taras Glek <tglek@xxxxxxxxxxx>
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxx>
> Cc: Michel Lespinasse <walken@xxxxxxxxxx>
> Cc: Minchan Kim <minchan@xxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx <linux-mm@xxxxxxxxx>
> Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
Just one minor nit below. Otherwise the patch looks good to me. So you
can add
Acked-by: Jan Kara <jack@xxxxxxx>

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@xxxxxxx>
SUSE Labs, CR
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