Re: [PATCH v3] slab_arena: Enhance slab_arena_create to support madvise hints

[Vladimir Davydov <vdavydov.dev@gmail.com>]

On Mon, May 13, 2019 at 11:01:26PM +0300, Cyrill Gorcunov wrote:
> The purpose of this extension is to be able to eliminate
> some of slab arenas from dumping, especially when huge
> amount of memory involves.
> 
> To keep backward compatibility we map flags passed into
> new SLAB_ARENA_x flags. To be able to distinguish old
> and new interfaces we reserve high bit of the integer
> value and remap flags internally to syscall compatible
> form.
> 
> Same time I have to modify build script to define
> _GNU_SOURCE symbol otherwise madvise bits won't be
> found.
> 
> Part-of https://github.com/tarantool/tarantool/issues/3509
> ---
> v2:
>   - Encode madvise hint inside slab_arena_create flags, for backward compatibility
>   - Enhance test to address dynamic slabs
>   - Enhance build procedure to test all falgs and functions we're interested in
> v3:
>   - Keep SLAB_ARENA_ flags inside struct slab_arena
>   - Use HAVE keyword in cmake
>   - Move madvise into madvise_checked helper
>   - Extend comment for SLAB_ARENA_ flags
> 
>  .gitignore           |   1 +
>  CMakeLists.txt       |  18 ++++++
>  small/config.h.cmake |  31 +++++++++++
>  small/slab_arena.c   |  68 +++++++++++++++++++----
>  small/slab_arena.h   |  23 +++++++-
>  test/slab_arena.c    | 128 +++++++++++++++++++++++++++++++++++++++++++

I'd also patch all places (tests, etc) where old flags (MAP_*) are used
to switch them to new flags. Sooner or later we should drop this compat
layer.

> diff --git a/small/slab_arena.c b/small/slab_arena.c
> index 26e2620..9f4baee 100644
> --- a/small/slab_arena.c
> +++ b/small/slab_arena.c
> @@ -41,17 +41,35 @@
>  #include <valgrind/valgrind.h>
>  #include <valgrind/memcheck.h>
>  
> -#if !defined(MAP_ANONYMOUS)
> -#define MAP_ANONYMOUS MAP_ANON
> +static void
> +madvise_checked(void *ptr, size_t size, int flags)
> +{
> +#ifdef TARANTOOL_SMALL_USE_MADVISE

It would be nice to have a warning in case MADV_DONTDUMP is unavailable.
It should be printed only once. May be, here, or, even better, in
Tarantool itself (via say_warn()).

> +	if (ptr && (flags & SLAB_ARENA_DONTDUMP)) {
> +		if (madvise(ptr, size, MADV_DONTDUMP)) {
> +			char *ignore_it;
> +			char buf[64];
> +
> +			ignore_it = strerror_r(errno, buf, sizeof(buf));
> +			(void)ignore_it;
> +
> +			fprintf(stderr, "Error in madvise(%p, %zu, 0x%x): %s\n",
> +				ptr, size, MADV_DONTDUMP, buf);
> +		}
> +	}
> +#else
> +	(void)ptr;
> +	(void)size;
> +	(void)flags;
>  #endif
> +}
>  
>  static void
>  munmap_checked(void *addr, size_t size)
>  {
>  	if (munmap(addr, size)) {
>  		char buf[64];
> -		intptr_t ignore_it = (intptr_t)strerror_r(errno, buf,
> -							  sizeof(buf));
> +		char *ignore_it = strerror_r(errno, buf, sizeof(buf));

This wouldn't compile on OS X. Please leave it as is. Same's fair for
madvise_checked.