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CyrIng

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From: France

Registered: 2010-07-17

Posts: 109

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CONFIG_INIT_ON_ALLOC_DEFAULT_ON and CONFIG_INIT_ON_FREE_DEFAULT_ON

Noticing in trunk/config that CONFIG_INIT_ON_ALLOC_DEFAULT_ON=y , will this be the default setting for next Arch kernel release ?

By zeroing the slab allocations, those options have a performance impact. See kernel commit

loqs

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Registered: 2014-03-06

Posts: 18,928

Re: CONFIG_INIT_ON_ALLOC_DEFAULT_ON and CONFIG_INIT_ON_FREE_DEFAULT_ON

https://git.archlinux.org/svntogit/pack … c2c395f22f

# CONFIG_INIT_ON_FREE_DEFAULT_ON is not set

hence is not on.  As the commit message you referenced and https://outflux.net/blog/archives/2019/ … inux-v5-3/ notes

The performance impact of the former under most workloads appears to be under 1%, if it’s measurable at all.

former being init_on_alloc.

CyrIng

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From: France

Registered: 2010-07-17

Posts: 109

Website

Re: CONFIG_INIT_ON_ALLOC_DEFAULT_ON and CONFIG_INIT_ON_FREE_DEFAULT_ON

I got it enable in trunk/config. So will it stay disable in repos/core-x86_64/config ...

What may cost in slab.c are the command line option conditions, even if staticaly built without CONFIG_INIT_ON_XXX

Such as:

if (unlikely(slab_want_init_on_alloc(flags, cachep)) && objp)
 		memset(objp, 0, cachep->object_size);

if (unlikely(slab_want_init_on_free(cachep)))
		memset(objp, 0, cachep->object_size);

loqs

Member

Registered: 2014-03-06

Posts: 18,928

Re: CONFIG_INIT_ON_ALLOC_DEFAULT_ON and CONFIG_INIT_ON_FREE_DEFAULT_ON

I got it enable in trunk/config. So will it stay disable in repos/core-x86_64/config ...

It is not in repos/core-x86_64 as there has been no new release since the change to trunk

What may cost in slab.c are the command line option conditions, even if staticaly built without CONFIG_INIT_ON_XXX

Such as:

if (unlikely(slab_want_init_on_alloc(flags, cachep)) && objp)
 		memset(objp, 0, cachep->object_size);

if (unlikely(slab_want_init_on_free(cachep)))
		memset(objp, 0, cachep->object_size);

You can benchmark with and without the following reverted so the functions you reference would never be called

-	if (mem_flags & __GFP_ZERO)
+	if (want_init_on_alloc(mem_flags))

and

+	if (want_init_on_free())
+		memset(vaddr, 0, pool->size);

CyrIng

Member

From: France

Registered: 2010-07-17

Posts: 109

Website

Re: CONFIG_INIT_ON_ALLOC_DEFAULT_ON and CONFIG_INIT_ON_FREE_DEFAULT_ON

As of version 5.3.12, linux/repos/core-x86_64/config now has the following definitions

CONFIG_INIT_ON_ALLOC_DEFAULT_ON=y
# CONFIG_INIT_ON_FREE_DEFAULT_ON is not set

To save a few cycles, I would have wished those macros conditionally compile or not the memset rather than branching.
https://elixir.bootlin.com/linux/latest … ab.c#L3259
https://elixir.bootlin.com/linux/latest … ub.c#L2746

loqs

Member

Registered: 2014-03-06

Posts: 18,928

Re: CONFIG_INIT_ON_ALLOC_DEFAULT_ON and CONFIG_INIT_ON_FREE_DEFAULT_ON

You could submit such a patch for that upstream.
How would you perform it though without removing support for the boot parameters init_on_alloc and init_on_free?