[PATCH 2/3] slab_arena: Provide slab_arena_madvise_create to madvice slabs
Vladimir Davydov
vdavydov.dev at gmail.com
Mon May 6 13:38:36 MSK 2019
[Cc += Alexander re tarantool/small backward compatibility]
On Wed, May 01, 2019 at 06:50:05PM +0300, Cyrill Gorcunov wrote:
> The purpose of this helper is to be able to eliminate
> some of slab arenas from dumping, especially when huge
> amount of memory involves.
>
> For this sake one should call slab_arena_madvise_create
> right after area's creation. Strictly speaking this helper
> may be called in any time but then some of already created
> slabs which are not inside preallocated area won't be
> madvised.
>
> Part of #3509
Again, please fix the link.
> ---
> https://github.com/tarantool/tarantool/issues/3509
>
> small/slab_arena.c | 49 ++++++++++++++++++++++++++++++++++++++++++++++
> small/slab_arena.h | 27 +++++++++++++++++++++++++
> 2 files changed, 76 insertions(+)
>
> diff --git a/small/slab_arena.c b/small/slab_arena.c
> index 26e2620..12f6198 100644
> --- a/small/slab_arena.c
> +++ b/small/slab_arena.c
> @@ -149,6 +149,9 @@ slab_arena_create(struct slab_arena *arena, struct quota *quota,
> arena->used = 0;
>
> arena->flags = flags;
> +#ifdef TARANTOOL_SMALL_HAS_MADVISE
> + pm_atomic_store(&arena->advice, MADV_NORMAL);
> +#endif
>
> if (arena->prealloc) {
> arena->arena = mmap_checked(arena->prealloc,
> @@ -205,6 +208,12 @@ slab_map(struct slab_arena *arena)
> __sync_sub_and_fetch(&arena->used, arena->slab_size);
> quota_release(arena->quota, arena->slab_size);
> }
> +
> +#ifdef TARANTOOL_SMALL_HAS_MADVISE
> + if (ptr && pm_atomic_load(&arena->advice) != MADV_NORMAL)
> + madvise(ptr, arena->slab_size, arena->advice);
> +#endif
> +
Why use atomic? The arena cannot be used until it's fully initialized.
> VALGRIND_MAKE_MEM_UNDEFINED(ptr, arena->slab_size);
> return ptr;
> }
> @@ -226,3 +235,43 @@ slab_arena_mprotect(struct slab_arena *arena)
> if (arena->arena)
> mprotect(arena->arena, arena->prealloc, PROT_READ);
> }
> +
> +#ifdef TARANTOOL_SMALL_HAS_MADVISE
> +/**
> + * slab_arena_madvise_create - Initialize madvise permanent strategy
> + * @arena: slab arena to madvise
> + * @advice: strategy (MADV_DONTDUMP, ...)
> + *
> + * This function setups @slab_arena strategy so that new memory
> + * allocation with mmap() call gets madvise() call with @advice.
> + *
> + * Note that we don't allow to change strategy once choosen because
> + * otherwise we need to walk over all possible slab cache entry.
> + *
> + * This function should be called right after the slab arena creation,
> + * otherwise if called later some of the non-preallocated slabs won't be
> + * madvise'd.
> + */
> +int
> +slab_arena_madvise_create(struct slab_arena *arena, int advice)
I don't see much point in changing madvise settings on the fly.
Let's instead allow to pass DONTDUMP flag at creation time.
This means we have to combine MAP_ and MADV_ flags. I guess it
was a bad idea to pass MAP_ flags directly to small_create() in
the first place. What about introducing small-specific flags like
SLAB_ARENA_SHARED
SLAB_ARENA_DONTDUMP
Come to think of it, I assume we don't even need to introduce
SLAB_ARENA_SHARED - we always pass MAP_PRIVATE to small_create().
Let's drop it, perhaps?
It will break backward compatibility, but I don't think it really
matters, as tarantool/small is only used by tarantool - it isn't
a big deal if we change its API. We only need to bump the version
number, I guess.
Alexander, please amend me if I'm wrong.
> +{
> + int expected = MADV_NORMAL;
> +
> + if (!pm_atomic_compare_exchange_strong(&arena->advice,
> + &expected, advice)) {
> + return -EBUSY;
> + }
> +
> + if (arena->arena)
> + return madvise(arena->arena, arena->prealloc, advice);
> + return 0;
> +}
> +#else
> +int
> +slab_arena_madvise_create(struct slab_arena *arena, int advice)
> +{
> + (void)arena;
> + (void)advice;
> + return -EINVAL;
> +}
> +#endif /* TARANTOOL_SMALL_HAS_MADVISE */
> diff --git a/small/slab_arena.h b/small/slab_arena.h
> index 364252f..4d86545 100644
> --- a/small/slab_arena.h
> +++ b/small/slab_arena.h
> @@ -31,8 +31,10 @@
> * SUCH DAMAGE.
> */
> #include "lf_lifo.h"
> +#include "config.h"
> #include <sys/mman.h>
> #include <limits.h>
> +#include <errno.h>
>
> #if defined(__cplusplus)
> extern "C" {
> @@ -97,6 +99,12 @@ struct slab_arena {
> * mmap() flags: MAP_SHARED or MAP_PRIVATE
> */
> int flags;
> +#ifdef TARANTOOL_SMALL_HAS_MADVISE
> + /**
> + * madvise() flag
> + */
> + int advice;
> +#endif
> };
>
> /** Initialize an arena. */
> @@ -120,6 +128,25 @@ slab_unmap(struct slab_arena *arena, void *ptr);
> void
> slab_arena_mprotect(struct slab_arena *arena);
>
> +/** madvise() all slabs. */
> +int
> +slab_arena_madvise_create(struct slab_arena *arena, int advice);
> +
> +/** handy helpers for slab_arena_madvise_create. */
> +#ifdef TARANTOOL_SMALL_HAS_MADVISE
> +static inline int
> +slab_arena_madvise_dontdump(struct slab_arena *arena)
> +{
> + return slab_arena_madvise_create(arena, MADV_DONTDUMP);
> +}
> +#else
> +static inline int
> +slab_arena_madvise_dontdump(struct slab_arena *arena)
> +{
> + return -EINVAL;
> +}
> +#endif
> +
> /**
> * Align a size - round up to nearest divisible by the given alignment.
> * Alignment must be a power of 2
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