linux-kernel - Re: [PATCH v4 18/22] slab: refill sheaves from all nodes

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Message-ID: <aXslbsUK1LXfx510@hyeyoo>
Date: Thu, 29 Jan 2026 18:16:30 +0900
From: Harry Yoo <harry.yoo@...cle.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Petr Tesarik <ptesarik@...e.com>, Christoph Lameter <cl@...two.org>,
        David Rientjes <rientjes@...gle.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>, Hao Li <hao.li@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Uladzislau Rezki <urezki@...il.com>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Alexei Starovoitov <ast@...nel.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev,
        bpf@...r.kernel.org, kasan-dev@...glegroups.com
Subject: Re: [PATCH v4 18/22] slab: refill sheaves from all nodes

On Fri, Jan 23, 2026 at 07:52:56AM +0100, Vlastimil Babka wrote:
> __refill_objects() currently only attempts to get partial slabs from the
> local node and then allocates new slab(s). Expand it to trying also
> other nodes while observing the remote node defrag ratio, similarly to
> get_any_partial().
> 
> This will prevent allocating new slabs on a node while other nodes have
> many free slabs. It does mean sheaves will contain non-local objects in
> that case. Allocations that care about specific node will still be
> served appropriately, but might get a slowpath allocation.
> 
> Like get_any_partial() we do observe cpuset_zone_allowed(), although we
> might be refilling a sheaf that will be then used from a different
> allocation context.
> 
> We can also use the resulting refill_objects() in
> __kmem_cache_alloc_bulk() for non-debug caches. This means
> kmem_cache_alloc_bulk() will get better performance when sheaves are
> exhausted. kmem_cache_alloc_bulk() cannot indicate a preferred node so
> it's compatible with sheaves refill in preferring the local node.
> Its users also have gfp flags that allow spinning, so document that
> as a requirement.
> 
> Reviewed-by: Suren Baghdasaryan <surenb@...gle.com>
> Reviewed-by: Hao Li <hao.li@...ux.dev>
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> ---

My only concern is that it allows sheaves with remote objects
to be returned back to the local barn by freeing local objects to them.

But the impact of that should be limited because remote frees bypass
sheaves layer anyway and we can revisit it if it causes a real problem.

That said,
Reviewed-by: Harry Yoo <harry.yoo@...cle.com>

-- 
Cheers,
Harry / Hyeonggon