From:   Thomas Gleixner <tglx@linutronix.de>
To:     Vlastimil Babka <vbabka@suse.cz>,
        kernel test robot <oliver.sang@intel.com>,
        Shanker Donthineni <sdonthineni@nvidia.com>
Cc:     oe-lkp@lists.linux.dev, lkp@intel.com,
        linux-kernel@vger.kernel.org, Marc Zyngier <maz@kernel.org>,
        Michael Walle <michael@walle.cc>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Hans de Goede <hdegoede@redhat.com>,
        Wolfram Sang <wsa+renesas@sang-engineering.com>,
        linux-mm@kvack.org, "Liam R. Howlett" <Liam.Howlett@oracle.com>,
        Matthew Wilcox <willy@infradead.org>,
        David Rientjes <rientjes@google.com>,
        Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Hyeonggon Yoo <42.hyeyoo@gmail.com>,
        Roman Gushchin <roman.gushchin@linux.dev>
Subject: Re: mm, slab/slub: Ensure kmem_cache_alloc_bulk() is available early
In-Reply-To: <8b7762c3-02be-a5c9-1c4d-507cfb51a15c@suse.cz>
References: <202302011308.f53123d2-oliver.sang@intel.com>
 <87o7qdzfay.ffs@tglx> <9a682773-df56-f36c-f582-e8eeef55d7f8@suse.cz>
 <875ycdwyx6.ffs@tglx> <871qn1wofe.ffs@tglx>
 <6c0b681e-97bc-d975-a8b9-500abdaaf0bc@suse.cz>
 <8b7762c3-02be-a5c9-1c4d-507cfb51a15c@suse.cz>
Date:   Tue, 07 Feb 2023 19:20:31 +0100
Message-ID: <87edr1uykw.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

On Tue, Feb 07 2023 at 15:47, Vlastimil Babka wrote:
> From 340d7c7b99f3e67780f6dec480ed1d27e6f325eb Mon Sep 17 00:00:00 2001
> From: Vlastimil Babka <vbabka@suse.cz>
> Date: Tue, 7 Feb 2023 15:34:53 +0100
> Subject: [PATCH] mm, slab/slub: remove notes that bulk alloc/free needs
>  interrupts enabled
>
> The slab functions kmem_cache_[alloc|free]_bulk() have been documented
> as requiring interrupts to be enabled, since their addition in 2015.
> It's unclear whether that was a fundamental restriction, or an attempt
> to save some cpu cycles by not having to save and restore the irq
> flags.

I don't think so. The restriction is rather meant to avoid huge
allocations in atomic context which causes latencies and also might
deplete the atomic reserves.

So I rather avoid that and enforce !ATOMIC mode despite the
local_irq_save/restore() change which is really only to accomodate with
early boot.

Thanks,

        tglx