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b=EquxJzNsDMw/0KeyNG4auMBMP0wP6kLplxNS0LhgoG8NQkbThad0GD4F+LIHwhjKQ lzhs7kZ8PLpagPgk0y1dQEr2sKoxFTF4VqcLYltNa+9zSNkt0qihVmYvm+T7RLeoJg 0skBcNxgWndYoIykw748fEC/y2ZM0C+tGqWjJ4uN4Vo+bDlXfcJlVBUnTuJU++ujdI AWXgAEYuzlFNBO/4/LHlsFkVJjlNRPHpJWiyQc13ZMYSpJPnZIMPqrriMGpFzGpFXq GrlYjW1py4ss8EaIqhW5r6lIrFAFskZdX6ngh+EV5yo8Eo01UwhN8e8q8Pn2aEFvW+ 7v4SNSGFvSfOA== Date: Wed, 7 Oct 2026 19:47:14 +0200 From: Harry Yoo To: Sang-Heon Jeon Cc: Andrew Morton , Vlastimil Babka , Christoph Lameter , David Rientjes , Hao Li , linux-mm@kvack.org, Roman Gushchin , stable@vger.kernel.org Subject: Re: [PATCH] mm/slub: clamp slab_min_order to MAX_PAGE_ORDER Message-ID: References: <20261007163403.1643768-1-ekffu200098@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261007163403.1643768-1-ekffu200098@gmail.com> X-Rspamd-Queue-Id: 6E22318000D X-Rspam-User: X-Rspamd-Server: rspam12 X-Stat-Signature: m6uun1ofm5z5sc9jey34zws33kwzjtap X-HE-Tag: 1791395241-287643 X-HE-Meta: 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 QwKgWbyy eJSmqFxMbCzQo67JrKIEp7PzQAZV8Nd1vnse8pohamTHAaoxzvdvN8Qfxd4+J/jKmFV4ipiZPpKEELY2N6KKC1FZRPV6CV4RZ5eajgDQN4NWBqPxOgEmqTRpcclzwZSxlZgIvPUlK2VQdUFShD7QSwtkNJfAT2TvQRDpWJUjNaZ8fT2RhFIWQktyFPt1OYrfsc0CcKrTEyzj38jX4juAimSJGt0mxFuSvOI9sAOkiJN8jiuHKInLgP6eYLSops8wQNG1x5GFSHHCx2XRq+W7bKOwhnJiykhFrxLRC4zPy2ZoUGwIVwIrclNvHTzFWWRUHYaInf8nFi4ALYEPqBLnPIX+nww== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Oct 08, 2026 at 01:34:02AM +0900, Sang-Heon Jeon wrote: > setup_slub_max_order() clamps slab_max_order to MAX_PAGE_ORDER, but > setup_slub_min_order() has no such clamp. > > The buddy allocator cannot allocate more than 2^MAX_PAGE_ORDER pages > at once, so slab_min_order above it makes no sense. > > If slab_min_order is set above MAX_PAGE_ORDER, it can even panic at > boot or invoke undefined behavior in order_objects(). > > So clamp slab_min_order to MAX_PAGE_ORDER as well. > > Fixes: 818cf5909701 ("slub: enforce MAX_ORDER") I think Fixes: should be the commit that introduced slub_min_order. > Cc: stable@vger.kernel.org And no need for Cc: stable? It's been there for decades and people should realize the kernel parameter is broken when it doesn't boot. Otherwise looks good to me. > Signed-off-by: Sang-Heon Jeon > --- > QEMU-based test results > > - Booted with "slab_min_order=20" > > 1) AS-IS (before fix) > [ 0.094926] mem auto-init: stack:all(zero), heap alloc:off, heap free:off > [ 0.097776] Kernel panic - not syncing: Creation of kmalloc slab kmem_cache_node size=64 failed. Reason -22 > [ 0.099542] CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 7.2.0 #1 PREEMPT(undef) > [ 0.100903] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 > [ 0.102607] Call Trace: > [ 0.103040] > [ 0.103417] vpanic+0x32a/0x4b0 > [ 0.103976] panic+0x5e/0x60 > [ 0.104491] create_boot_cache+0xe3/0xf0 > [ 0.105194] kmem_cache_init+0x12d/0x410 > [ 0.105890] ? mem_init+0x1fc/0x210 > [ 0.106521] mm_core_init+0xba/0x140 > [ 0.107153] start_kernel+0x441/0x8b0 > [ 0.107814] x86_64_start_reservations+0x18/0x30 > [ 0.108638] x86_64_start_kernel+0x10c/0x120 > [ 0.109401] common_startup_64+0x13e/0x158 > [ 0.110145] > [ 0.110584] ---[ end Kernel panic - not syncing: Creation of kmalloc slab kmem_cache_node size=64 failed. Reason -22 ]--- > > 2) TO-BE (after fix) > [ 0.008976] mem auto-init: stack:all(zero), heap alloc:off, heap free:off > [ 0.011366] SLUB: HWalign=64, Order=10-10, MinObjects=0, CPUs=4, Nodes=1 > > Also, I'm not sure about the Fixes commit. Please change it if you know > a better one. > > --- > mm/slub.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/mm/slub.c b/mm/slub.c > index 1559cbace469..8400df7c222e 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -8354,6 +8354,8 @@ static int __init setup_slub_min_order(const char *str, const struct kernel_para > if (ret) > return ret; > > + slub_min_order = min_t(unsigned int, slub_min_order, MAX_PAGE_ORDER); > + > if (slub_min_order > slub_max_order) > slub_max_order = slub_min_order; > > > base-commit: d755441b7672c74f29d1241ffdd2b067ecab1ca0 > -- > 2.43.0 > -- Cheers, Harry / Hyeonggon