Re: [PATCH] mm/huge_memory: use new hashtable implementation

[Sasha Levin <levinsasha928@gmail.com>]

Ping?

On Fri, Dec 21, 2012 at 1:59 PM, Sasha Levin <sasha.levin@oracle.com> wrote:
> Switch hugemem to use the new hashtable implementation. This reduces the
> amount of generic unrelated code in the hugemem.
>
> This also removes the dymanic allocation of the hash table. The upside is that
> we save a pointer dereference when accessing the hashtable, but we lose 8KB
> if CONFIG_TRANSPARENT_HUGEPAGE is enabled but the processor doesn't
> support hugepages.
>
> This patch depends on d9b482c ("hashtable: introduce a small and naive
> hashtable") which was merged in v3.6.
>
> Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
> ---
> Changes in v2:
>  - Addressed comments by David Rientjes.
>
>  mm/huge_memory.c | 54 +++++++++---------------------------------------------
>  1 file changed, 9 insertions(+), 45 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 9e894ed..f62654c 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -20,6 +20,7 @@
>  #include <linux/mman.h>
>  #include <linux/pagemap.h>
>  #include <linux/migrate.h>
> +#include <linux/hashtable.h>
>
>  #include <asm/tlb.h>
>  #include <asm/pgalloc.h>
> @@ -62,12 +63,11 @@ static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
>  static unsigned int khugepaged_max_ptes_none __read_mostly = HPAGE_PMD_NR-1;
>
>  static int khugepaged(void *none);
> -static int mm_slots_hash_init(void);
>  static int khugepaged_slab_init(void);
> -static void khugepaged_slab_free(void);
>
> -#define MM_SLOTS_HASH_HEADS 1024
> -static struct hlist_head *mm_slots_hash __read_mostly;
> +#define MM_SLOTS_HASH_BITS 10
> +static __read_mostly DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
> +
>  static struct kmem_cache *mm_slot_cache __read_mostly;
>
>  /**
> @@ -634,12 +634,6 @@ static int __init hugepage_init(void)
>         if (err)
>                 goto out;
>
> -       err = mm_slots_hash_init();
> -       if (err) {
> -               khugepaged_slab_free();
> -               goto out;
> -       }
> -
>         register_shrinker(&huge_zero_page_shrinker);
>
>         /*
> @@ -1893,12 +1887,6 @@ static int __init khugepaged_slab_init(void)
>         return 0;
>  }
>
> -static void __init khugepaged_slab_free(void)
> -{
> -       kmem_cache_destroy(mm_slot_cache);
> -       mm_slot_cache = NULL;
> -}
> -
>  static inline struct mm_slot *alloc_mm_slot(void)
>  {
>         if (!mm_slot_cache)     /* initialization failed */
> @@ -1911,47 +1899,23 @@ static inline void free_mm_slot(struct mm_slot *mm_slot)
>         kmem_cache_free(mm_slot_cache, mm_slot);
>  }
>
> -static int __init mm_slots_hash_init(void)
> -{
> -       mm_slots_hash = kzalloc(MM_SLOTS_HASH_HEADS * sizeof(struct hlist_head),
> -                               GFP_KERNEL);
> -       if (!mm_slots_hash)
> -               return -ENOMEM;
> -       return 0;
> -}
> -
> -#if 0
> -static void __init mm_slots_hash_free(void)
> -{
> -       kfree(mm_slots_hash);
> -       mm_slots_hash = NULL;
> -}
> -#endif
> -
>  static struct mm_slot *get_mm_slot(struct mm_struct *mm)
>  {
>         struct mm_slot *mm_slot;
> -       struct hlist_head *bucket;
>         struct hlist_node *node;
>
> -       bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
> -                               % MM_SLOTS_HASH_HEADS];
> -       hlist_for_each_entry(mm_slot, node, bucket, hash) {
> +       hash_for_each_possible(mm_slots_hash, mm_slot, node, hash, (unsigned long) mm)
>                 if (mm == mm_slot->mm)
>                         return mm_slot;
> -       }
> +
>         return NULL;
>  }
>
>  static void insert_to_mm_slots_hash(struct mm_struct *mm,
>                                     struct mm_slot *mm_slot)
>  {
> -       struct hlist_head *bucket;
> -
> -       bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
> -                               % MM_SLOTS_HASH_HEADS];
>         mm_slot->mm = mm;
> -       hlist_add_head(&mm_slot->hash, bucket);
> +       hash_add(mm_slots_hash, &mm_slot->hash, (long)mm);
>  }
>
>  static inline int khugepaged_test_exit(struct mm_struct *mm)
> @@ -2020,7 +1984,7 @@ void __khugepaged_exit(struct mm_struct *mm)
>         spin_lock(&khugepaged_mm_lock);
>         mm_slot = get_mm_slot(mm);
>         if (mm_slot && khugepaged_scan.mm_slot != mm_slot) {
> -               hlist_del(&mm_slot->hash);
> +               hash_del(&mm_slot->hash);
>                 list_del(&mm_slot->mm_node);
>                 free = 1;
>         }
> @@ -2469,7 +2433,7 @@ static void collect_mm_slot(struct mm_slot *mm_slot)
>
>         if (khugepaged_test_exit(mm)) {
>                 /* free mm_slot */
> -               hlist_del(&mm_slot->hash);
> +               hash_del(&mm_slot->hash);
>                 list_del(&mm_slot->mm_node);
>
>                 /*
> --
> 1.8.0
>
> --
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