Re: Deprecating and removing SLOB

From: Yosry Ahmed <yosryahmed@google.com>
To: Roman Gushchin <roman.gushchin@linux.dev>,
	David Rientjes <rientjes@google.com>,
	Greg Thelen <gthelen@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>,
	Christoph Lameter <cl@linux.com>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	Pekka Enberg <penberg@kernel.org>,
	Hyeonggon Yoo <42.hyeyoo@gmail.com>,
	Matthew Wilcox <willy@infradead.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Rustam Kovhaev <rkovhaev@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: Deprecating and removing SLOB
Date: Tue, 8 Nov 2022 12:13:50 -0800	[thread overview]
Message-ID: <CAJD7tkaqrz8sGqgbyfQHU_NM3O=a_0bqSHB0gGYRB7Kj+w_05w@mail.gmail.com> (raw)
In-Reply-To: <Y2qkIrk+a9v7tAQZ@P9FQF9L96D.lan>

On Tue, Nov 8, 2022 at 10:47 AM Roman Gushchin <roman.gushchin@linux.dev> wrote:
>
> On Tue, Nov 08, 2022 at 04:55:29PM +0100, Vlastimil Babka wrote:
> > Hi,
> >
> > as we all know, we currently have three slab allocators. As we discussed at
> > LPC [1], it is my hope that one of these allocators has a future, and two of
> > them do not.
> >
> > The unsurprising reasons include code maintenance burden, other features
> > compatible with only a subset of allocators (or more effort spent on the
> > features), blocking API improvements (more on that below), and my inability
> > to pronounce SLAB and SLUB in a properly distinguishable way, without
> > resorting to spelling out the letters.
> >
> > I think (but may be proven wrong) that SLOB is the easier target of the two
> > to be removed, so I'd like to focus on it first.
>
> Great!
>
> SLOB is not supported by the kernel memory accounting code, so if we'll
> deprecate SLOB, we can remove all those annoying ifndefs.
>
> But I wonder if we can deprecate SLAB too? Or at least use the moment to
> ask every non-SLUB user on why they can't/don't want to use SLUB.
> Are there any known advantages of SLAB over SLUB?

We use SLAB at Google, but I am not the right person to answer the
question of why we can't/don't use SLUB. Adding Greg here who recently
looked into this and might have answers. I see David is already
tagged, he might have a good answer as well.

>
> Also, for memory-constrained users we might want to add some guide on how
> to configure SLUB to minimize the memory footprint.
>
> Thank you!
>
> Roman
>