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    SubjectRE: [PATCH 3.2.0-rc1 2/3] MM hook for page allocation and release
    Date
    Hi,

    I agree that hooking alloc_pages is ugly way. So alternatives I see:

    - shrinkers (as e.g. Android OOM used) but shrink_slab called only from try_to_free_pages only if we are on slow reclaim path on memory allocation, so it cannot be used for e.g. 75% memory tracking or when pages released to notify user space that we are OK. But according to easy to use it will be the best approach.

    - memcg-kind of changes like mem_cgroup_newpage_charge/uncharge_page but without blocking decision making logic. Seems to me more changes. Threshold currently in memcg set 128 pages per CPU, that is quite often for level tracking needs.

    - tracking situation using timer? Maybe not due to will impact battery.

    With Best Wishes,
    Leonid


    -----Original Message-----
    From: ext KAMEZAWA Hiroyuki [mailto:kamezawa.hiroyu@jp.fujitsu.com]
    Sent: 05 January, 2012 09:00
    To: Moiseichuk Leonid (Nokia-MP/Helsinki)
    Cc: linux-mm@kvack.org; linux-kernel@vger.kernel.org; cesarb@cesarb.net; emunson@mgebm.net; penberg@kernel.org; aarcange@redhat.com; riel@redhat.com; mel@csn.ul.ie; rientjes@google.com; dima@android.com; gregkh@suse.de; rebecca@android.com; san@google.com; akpm@linux-foundation.org; Jaaskelainen Vesa (Nokia-MP/Helsinki)
    Subject: Re: [PATCH 3.2.0-rc1 2/3] MM hook for page allocation and release

    On Wed, 4 Jan 2012 19:21:55 +0200
    Leonid Moiseichuk <leonid.moiseichuk@nokia.com> wrote:

    > That is required by Used Memory Meter (UMM) pseudo-device to track
    > memory utilization in system. It is expected that hook MUST be very
    > light to prevent performance impact on the hot allocation path.
    > Accuracy of number managed pages does not expected to be absolute but
    > fact of allocation or deallocation must be registered.
    >
    > Signed-off-by: Leonid Moiseichuk <leonid.moiseichuk@nokia.com>

    I never like arbitrary hooks to alloc_pages().
    Could you find another way ?

    Hmm. memcg uses per-cpu counters for counting event of alloc/free and trigger threashold check per 128 event on a cpu.


    Thanks,
    -Kame


    > ---
    > include/linux/mm.h | 15 +++++++++++++++
    > mm/Kconfig | 8 ++++++++
    > mm/page_alloc.c | 31 +++++++++++++++++++++++++++++++
    > 3 files changed, 54 insertions(+), 0 deletions(-)
    >
    > diff --git a/include/linux/mm.h b/include/linux/mm.h index
    > 3dc3a8c..d133f73 100644
    > --- a/include/linux/mm.h
    > +++ b/include/linux/mm.h
    > @@ -1618,6 +1618,21 @@ extern int soft_offline_page(struct page *page,
    > int flags);
    >
    > extern void dump_page(struct page *page);
    >
    > +#ifdef CONFIG_MM_ALLOC_FREE_HOOK
    > +/*
    > + * Hook function type which called when some pages allocated or released.
    > + * Value of nr_pages is positive for post-allocation calls and
    > +negative
    > + * after free.
    > + */
    > +typedef void (*mm_alloc_free_hook_t)(int nr_pages);
    > +
    > +/*
    > + * Setups specified hook function for tracking pages allocation.
    > + * Returns value of old hook to organize chains of calls if necessary.
    > + */
    > +mm_alloc_free_hook_t set_mm_alloc_free_hook(mm_alloc_free_hook_t
    > +hook); #endif
    > +
    > #if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)
    > extern void clear_huge_page(struct page *page,
    > unsigned long addr,
    > diff --git a/mm/Kconfig b/mm/Kconfig
    > index 011b110..2aaa1e9 100644
    > --- a/mm/Kconfig
    > +++ b/mm/Kconfig
    > @@ -373,3 +373,11 @@ config CLEANCACHE
    > in a negligible performance hit.
    >
    > If unsure, say Y to enable cleancache
    > +
    > +config MM_ALLOC_FREE_HOOK
    > + bool "Enable callback support for pages allocation and releasing"
    > + default n
    > + help
    > + Required for some features like used memory meter.
    > + If unsure, say N to disable alloc/free hook.
    > +
    > diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 9dd443d..9307800
    > 100644
    > --- a/mm/page_alloc.c
    > +++ b/mm/page_alloc.c
    > @@ -236,6 +236,30 @@ static void set_pageblock_migratetype(struct page
    > *page, int migratetype)
    >
    > bool oom_killer_disabled __read_mostly;
    >
    > +#ifdef CONFIG_MM_ALLOC_FREE_HOOK
    > +static atomic_long_t alloc_free_hook __read_mostly =
    > +ATOMIC_LONG_INIT(0);
    > +
    > +mm_alloc_free_hook_t set_mm_alloc_free_hook(mm_alloc_free_hook_t
    > +hook) {
    > + const mm_alloc_free_hook_t old_hook =
    > + (mm_alloc_free_hook_t)atomic_long_read(&alloc_free_hook);
    > +
    > + atomic_long_set(&alloc_free_hook, (long)hook);
    > + pr_info("MM alloc/free hook set to 0x%p (was 0x%p)\n", hook,
    > +old_hook);
    > +
    > + return old_hook;
    > +}
    > +EXPORT_SYMBOL(set_mm_alloc_free_hook);
    > +
    > +static inline void call_alloc_free_hook(int pages) {
    > + const mm_alloc_free_hook_t hook =
    > + (mm_alloc_free_hook_t)atomic_long_read(&alloc_free_hook);
    > + if (hook)
    > + hook(pages);
    > +}
    > +#endif
    > +
    > #ifdef CONFIG_DEBUG_VM
    > static int page_outside_zone_boundaries(struct zone *zone, struct
    > page *page) { @@ -2298,6 +2322,10 @@ __alloc_pages_nodemask(gfp_t
    > gfp_mask, unsigned int order,
    > put_mems_allowed();
    >
    > trace_mm_page_alloc(page, order, gfp_mask, migratetype);
    > +#ifdef CONFIG_MM_ALLOC_FREE_HOOK
    > + call_alloc_free_hook(1 << order);
    > +#endif
    > +
    > return page;
    > }
    > EXPORT_SYMBOL(__alloc_pages_nodemask);
    > @@ -2345,6 +2373,9 @@ void __free_pages(struct page *page, unsigned int order)
    > free_hot_cold_page(page, 0);
    > else
    > __free_pages_ok(page, order);
    > +#ifdef CONFIG_MM_ALLOC_FREE_HOOK
    > + call_alloc_free_hook(-(1 << order)); #endif
    > }
    > }
    >
    > --
    > 1.7.7.3
    >
    >



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