Re: [RFC v2] slab_arena: Enhance slab_arena_create to support madvise hints

[Cyrill Gorcunov <gorcunov@gmail.com>]

On Mon, May 13, 2019 at 01:06:42PM +0300, Vladimir Davydov wrote:
> >  
> > +set(CMAKE_REQUIRED_DEFINITIONS "-D_GNU_SOURCE")
> > +
> > +check_symbol_exists(MAP_ANON sys/mman.h TARANTOOL_SMALL_HAVE_MAP_ANON)
> > +check_symbol_exists(MAP_ANONYMOUS sys/mman.h TARANTOOL_SMALL_HAVE_MAP_ANONYMOUS)
> > +
> > +check_function_exists(madvise TARANTOOL_SMALL_HAS_MADVISE)
> 
> HAS/HAVE - please be consistent in naming.

OK

> > +check_symbol_exists(MADV_NORMAL sys/mman.h TARANTOOL_SMALL_HAS_MADV_NORMAL)
> > +check_symbol_exists(MADV_DONTDUMP sys/mman.h TARANTOOL_SMALL_HAS_MADV_DONTDUMP)
> 
> Do we really need to check all of that? Is a check for MADV_DONTDUMP not
> enough?

Well, strictly speaking we should check each definition we use, because I'm
not sure if MADV_NORMAL defined on other than linux environments.

> > +
> > +#ifdef TARANTOOL_SMALL_USE_MADVISE
> > +	if (slab_flags & SLAB_ARENA_DONTDUMP)
> > +		arena->madv_flag = MADV_DONTDUMP;
> > +#endif
> 
> May be, better store slab_flags in arena and convert them to
> mmap/madvise flags when necessary? Would be one variable instead
> of two.

Sounds reasonable, will do.

> > +
> > +#ifdef TARANTOOL_SMALL_USE_MADVISE
> > +	if (ptr && arena->madv_flag != MADV_NORMAL)
> > +		madvise(ptr, arena->slab_size, arena->madv_flag);
> > +#endif
> > +
> 
> I'd move this code to a helper function to avoid code duplication in
> slab_arena_create/slab_map.

OK

> >  
> > +/**
> > + * Backward compatible flags to be used with slab_arena_create().
> 
> Please elaborate the comment: explain how this backward compatibility
> hack works, what it's needed for.

Sure


	Cyrill