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Message-ID: <532775AD.90007@linaro.org>
Date: Mon, 17 Mar 2014 15:22:37 -0700
From: John Stultz <john.stultz@...aro.org>
To: Jan Kara <jack@...e.cz>
CC: LKML <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Android Kernel Team <kernel-team@...roid.com>,
Johannes Weiner <hannes@...xchg.org>,
Robert Love <rlove@...gle.com>, Mel Gorman <mel@....ul.ie>,
Hugh Dickins <hughd@...gle.com>, Dave Hansen <dave@...1.net>,
Rik van Riel <riel@...hat.com>,
Dmitry Adamushko <dmitry.adamushko@...il.com>,
Neil Brown <neilb@...e.de>,
Andrea Arcangeli <aarcange@...hat.com>,
Mike Hommey <mh@...ndium.org>, Taras Glek <tglek@...illa.com>,
Dhaval Giani <dgiani@...illa.com>,
KOSAKI Motohiro <kosaki.motohiro@...il.com>,
Michel Lespinasse <walken@...gle.com>,
Minchan Kim <minchan@...nel.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH 2/3] vrange: Add purged page detection on setting memory
non-volatile
On 03/17/2014 02:39 AM, Jan Kara wrote:
> On Fri 14-03-14 11:33:32, 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.
> Some minor comments below...
>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: Android Kernel Team <kernel-team@...roid.com>
>> Cc: Johannes Weiner <hannes@...xchg.org>
>> Cc: Robert Love <rlove@...gle.com>
>> Cc: Mel Gorman <mel@....ul.ie>
>> Cc: Hugh Dickins <hughd@...gle.com>
>> Cc: Dave Hansen <dave@...1.net>
>> Cc: Rik van Riel <riel@...hat.com>
>> Cc: Dmitry Adamushko <dmitry.adamushko@...il.com>
>> Cc: Neil Brown <neilb@...e.de>
>> Cc: Andrea Arcangeli <aarcange@...hat.com>
>> Cc: Mike Hommey <mh@...ndium.org>
>> Cc: Taras Glek <tglek@...illa.com>
>> Cc: Dhaval Giani <dgiani@...illa.com>
>> Cc: Jan Kara <jack@...e.cz>
>> Cc: KOSAKI Motohiro <kosaki.motohiro@...il.com>
>> Cc: Michel Lespinasse <walken@...gle.com>
>> Cc: Minchan Kim <minchan@...nel.org>
>> Cc: linux-mm@...ck.org <linux-mm@...ck.org>
>> Signed-off-by: John Stultz <john.stultz@...aro.org>
>> ---
>> include/linux/swap.h | 15 +++++++++++--
>> include/linux/vrange.h | 13 ++++++++++++
>> mm/vrange.c | 57 ++++++++++++++++++++++++++++++++++++++++++++++++++
>> 3 files changed, 83 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/vrange.h b/include/linux/vrange.h
>> index 652396b..c4a1616 100644
>> --- a/include/linux/vrange.h
>> +++ b/include/linux/vrange.h
>> @@ -1,7 +1,20 @@
>> #ifndef _LINUX_VRANGE_H
>> #define _LINUX_VRANGE_H
>>
>> +#include <linux/swap.h>
>> +#include <linux/swapops.h>
>> +
>> #define VRANGE_NONVOLATILE 0
>> #define VRANGE_VOLATILE 1
>>
>> +static inline swp_entry_t swp_entry_mk_vrange_purged(void)
>> +{
>> + return swp_entry(SWP_VRANGE_PURGED, 0);
>> +}
>> +
>> +static inline int entry_is_vrange_purged(swp_entry_t entry)
>> +{
>> + return swp_type(entry) == SWP_VRANGE_PURGED;
>> +}
>> +
>> #endif /* _LINUX_VRANGE_H */
>> diff --git a/mm/vrange.c b/mm/vrange.c
>> index acb4356..844571b 100644
>> --- a/mm/vrange.c
>> +++ b/mm/vrange.c
>> @@ -8,6 +8,60 @@
>> #include <linux/mm_inline.h>
>> #include "internal.h"
>>
>> +struct vrange_walker {
>> + struct vm_area_struct *vma;
>> + int pages_purged;
> Maybe call this 'was_page_purged'? To better suggest the value is bool
> and not a number of pages... Or make that 'bool' instead of 'int'?
Yea, page_was_purged sounds good to me. Thanks for pointing out the
ambiguity. Similarly the
entry_is_vrange_purged/swp_entry_mk_vrange_purged functions are a little inconsistently named.
>
>> +};
>> +
>> +static int vrange_pte_range(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(entry_is_vrange_purged(vrange_entry))) {
>> + vw->pages_purged = 1;
>> + break;
>> + }
>> + }
>> + }
>> + pte_unmap_unlock(pte - 1, ptl);
>> + cond_resched();
>> +
>> + return 0;
>> +}
>> +
>> +static unsigned long vrange_check_purged(struct mm_struct *mm,
> What's the point of this function returning ulong when everything else
> expects 'int'?
Thanks, I'll fix that.
>> + struct vm_area_struct *vma,
>> + unsigned long start,
>> + unsigned long end)
>> +{
>> + struct vrange_walker vw;
>> + struct mm_walk vrange_walk = {
>> + .pmd_entry = vrange_pte_range,
>> + .mm = vma->vm_mm,
>> + .private = &vw,
>> + };
>> + vw.pages_purged = 0;
>> + vw.vma = vma;
>> +
>> + walk_page_range(start, end, &vrange_walk);
>> +
>> + return vw.pages_purged;
>> +
>> +}
>> +
>> static ssize_t do_vrange(struct mm_struct *mm, unsigned long start,
>> unsigned long end, int mode, int *purged)
>> {
>> @@ -57,6 +111,9 @@ static ssize_t do_vrange(struct mm_struct *mm, unsigned long start,
>> break;
>> case VRANGE_NONVOLATILE:
>> new_flags &= ~VM_VOLATILE;
>> + lpurged |= vrange_check_purged(mm, vma,
>> + vma->vm_start,
>> + vma->vm_end);
> Hum, why don't you actually just call vrange_check_purge() once for the
> whole syscall range? walk_page_range() seems to handle multiple vmas just
> fine...
>
Another good suggestion!
Thanks!
-john
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