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Date: Fri, 12 Jun 2015 19:46:55 +0100
From: Mark Williamson <mwilliamson@...o-software.com>
To: Konstantin Khlebnikov <koct9i@...il.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
Linux API <linux-api@...r.kernel.org>,
kernel list <linux-kernel@...r.kernel.org>,
"Kirill A. Shutemov" <kirill@...temov.name>
Subject: Re: [PATCH v3 2/4] pagemap: add mmap-exclusive bit for marking pages
mapped only here
This looks good from our side - thanks!
Reviewed-by: mwilliamson@...o-software.com
Tested-by: mwilliamson@...o-software.com
On Tue, Jun 9, 2015 at 9:00 PM, Konstantin Khlebnikov <koct9i@...il.com> wrote:
> From: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
>
> This patch sets bit 56 in pagemap if this page is mapped only once.
> It allows to detect exclusively used pages without exposing PFN:
>
> present file exclusive state
> 0 0 0 non-present
> 1 1 0 file page mapped somewhere else
> 1 1 1 file page mapped only here
> 1 0 0 anon non-CoWed page (shared with parent/child)
> 1 0 1 anon CoWed page (or never forked)
>
> CoWed pages in MAP_FILE|MAP_PRIVATE areas are anon in this context.
>
> Mmap-exclusive bit doesn't reflect potential page-sharing via swapcache:
> page could be mapped once but has several swap-ptes which point to it.
> Application could detect that by swap bit in pagemap entry and touch
> that pte via /proc/pid/mem to get real information.
>
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
> Link: http://lkml.kernel.org/r/CAEVpBa+_RyACkhODZrRvQLs80iy0sqpdrd0AaP_-tgnX3Y9yNQ@mail.gmail.com
>
> ---
>
> v2:
> * handle transparent huge pages
> * invert bit and rename shared -> exclusive (less confusing name)
> ---
> Documentation/vm/pagemap.txt | 3 ++-
> fs/proc/task_mmu.c | 10 ++++++++++
> tools/vm/page-types.c | 12 ++++++++++++
> 3 files changed, 24 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/vm/pagemap.txt b/Documentation/vm/pagemap.txt
> index 6bfbc17..3cfbbb3 100644
> --- a/Documentation/vm/pagemap.txt
> +++ b/Documentation/vm/pagemap.txt
> @@ -16,7 +16,8 @@ There are three components to pagemap:
> * Bits 0-4 swap type if swapped
> * Bits 5-54 swap offset if swapped
> * Bit 55 pte is soft-dirty (see Documentation/vm/soft-dirty.txt)
> - * Bits 56-60 zero
> + * Bit 56 page exlusively mapped
> + * Bits 57-60 zero
> * Bit 61 page is file-page or shared-anon
> * Bit 62 page swapped
> * Bit 63 page present
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 21bc251..b02e38f 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -982,6 +982,7 @@ struct pagemapread {
> #define PM_STATUS2(v2, x) (__PM_PSHIFT(v2 ? x : PAGE_SHIFT))
>
> #define __PM_SOFT_DIRTY (1LL)
> +#define __PM_MMAP_EXCLUSIVE (2LL)
> #define PM_PRESENT PM_STATUS(4LL)
> #define PM_SWAP PM_STATUS(2LL)
> #define PM_FILE PM_STATUS(1LL)
> @@ -1074,6 +1075,8 @@ static void pte_to_pagemap_entry(pagemap_entry_t *pme, struct pagemapread *pm,
>
> if (page && !PageAnon(page))
> flags |= PM_FILE;
> + if (page && page_mapcount(page) == 1)
> + flags2 |= __PM_MMAP_EXCLUSIVE;
> if ((vma->vm_flags & VM_SOFTDIRTY))
> flags2 |= __PM_SOFT_DIRTY;
>
> @@ -1119,6 +1122,13 @@ static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
> else
> pmd_flags2 = 0;
>
> + if (pmd_present(*pmd)) {
> + struct page *page = pmd_page(*pmd);
> +
> + if (page_mapcount(page) == 1)
> + pmd_flags2 |= __PM_MMAP_EXCLUSIVE;
> + }
> +
> for (; addr != end; addr += PAGE_SIZE) {
> unsigned long offset;
> pagemap_entry_t pme;
> diff --git a/tools/vm/page-types.c b/tools/vm/page-types.c
> index 8bdf16b..3a9f193 100644
> --- a/tools/vm/page-types.c
> +++ b/tools/vm/page-types.c
> @@ -70,9 +70,12 @@
> #define PM_PFRAME(x) ((x) & PM_PFRAME_MASK)
>
> #define __PM_SOFT_DIRTY (1LL)
> +#define __PM_MMAP_EXCLUSIVE (2LL)
> #define PM_PRESENT PM_STATUS(4LL)
> #define PM_SWAP PM_STATUS(2LL)
> +#define PM_FILE PM_STATUS(1LL)
> #define PM_SOFT_DIRTY __PM_PSHIFT(__PM_SOFT_DIRTY)
> +#define PM_MMAP_EXCLUSIVE __PM_PSHIFT(__PM_MMAP_EXCLUSIVE)
>
>
> /*
> @@ -100,6 +103,8 @@
> #define KPF_SLOB_FREE 49
> #define KPF_SLUB_FROZEN 50
> #define KPF_SLUB_DEBUG 51
> +#define KPF_FILE 62
> +#define KPF_MMAP_EXCLUSIVE 63
>
> #define KPF_ALL_BITS ((uint64_t)~0ULL)
> #define KPF_HACKERS_BITS (0xffffULL << 32)
> @@ -149,6 +154,9 @@ static const char * const page_flag_names[] = {
> [KPF_SLOB_FREE] = "P:slob_free",
> [KPF_SLUB_FROZEN] = "A:slub_frozen",
> [KPF_SLUB_DEBUG] = "E:slub_debug",
> +
> + [KPF_FILE] = "F:file",
> + [KPF_MMAP_EXCLUSIVE] = "1:mmap_exclusive",
> };
>
>
> @@ -452,6 +460,10 @@ static uint64_t expand_overloaded_flags(uint64_t flags, uint64_t pme)
>
> if (pme & PM_SOFT_DIRTY)
> flags |= BIT(SOFTDIRTY);
> + if (pme & PM_FILE)
> + flags |= BIT(FILE);
> + if (pme & PM_MMAP_EXCLUSIVE)
> + flags |= BIT(MMAP_EXCLUSIVE);
>
> return flags;
> }
>
--
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