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Tue, 13 Jan 2026 05:16:27 -0500 X-MC-Unique: bLVTTVX1Pm2AONjrwC1DFw-1 X-Mimecast-MFC-AGG-ID: bLVTTVX1Pm2AONjrwC1DFw_1768299385 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id A42C51956046; Tue, 13 Jan 2026 10:16:24 +0000 (UTC) Received: from localhost (unknown [10.72.112.148]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id C3CB330001A2; Tue, 13 Jan 2026 10:16:22 +0000 (UTC) Date: Tue, 13 Jan 2026 18:16:18 +0800 From: Baoquan He To: Robin Murphy Cc: m.szyprowski@samsung.com, akpm@linux-foundation.org, vbabka@suse.cz, david@kernel.org, iommu@lists.linux-foundation.org, linux-mm@kvack.org, vladimir.kondratiev@mobileye.com, s-adivi@ti.com, linux-kernel@vger.kernel.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, rppt@kernel.org, surenb@google.com, mhocko@suse.com, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com Subject: Re: [PATCH 3/3] dma/pool: Avoid allocating redundant pools Message-ID: References: <8ab8d8a620dee0109f33f5cb63d6bfeed35aac37.1768230104.git.robin.murphy@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8ab8d8a620dee0109f33f5cb63d6bfeed35aac37.1768230104.git.robin.murphy@arm.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 X-Rspam-User: X-Stat-Signature: unz5ytrwfbf3ku64g3k1fza36omhd8n3 X-Rspamd-Queue-Id: D1957140006 X-Rspamd-Server: rspam04 X-HE-Tag: 1768299391-412236 X-HE-Meta: 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 IGRZ3pQR dhbLWLCCSpjTdWDO66BRYWnKVdA90CouCwTSH+cHMGU0SBKPz1LnJVPptWeEcJeGjJ4PvyNGHzMbkQmjYR7C3TGZD8VfqwT0ReT00LHVmMZGCXqzgduG/8jPmXsFixOfwaJJBVOEE+5kk+bFKQ/IESjB3iZhyPpfbPFH+VibZ8Rq+7EUpQH4QbCGhZgKieopRJGIlkRMpxa3071tPZKVcH6KjJuKQHceN/0xH+dBVrCBVCZoxqrmx517+QLbIXEuO0a/i40E/5yIsGq9mXi7Px5qhZN4oPTbyKyx/NKXrOxYnpNmmhYeORJPLbM08kDLaq+hQtkHtTlVFnvYTmFpLL8KzsjTAXn0WsCMCjIEsD8Pv+UxQEt4jN9HGfaBl1cuf0DwJkzlQDN/CvdVgB7n5xq20rxA1LW9vWO0TOeZWJ/uWMRjmbVIcTSzRaob5/KdtUlpZKGQGqurkZGWGqL/TL8ORcA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 01/12/26 at 03:46pm, Robin Murphy wrote: > On smaller systems, e.g. embedded arm64, it is common for all memory > to end up in ZONE_DMA32 or even ZONE_DMA. In such cases it is redundant This is true and the whole series looks great to me. Do we need adjust warn_alloc() to handle empty DMA32 zone too like empty DMA zone case? > to allocate a nominal pool for an empty higher zone that just ends up > coming from a lower zone that should already have its own pool anyway. > We already have logic to skip allocating a ZONE_DMA pool when that is > empty, so generalise that to save memory in the case of other zones too. > > Signed-off-by: Robin Murphy > --- > kernel/dma/pool.c | 19 ++++++++++++++----- > 1 file changed, 14 insertions(+), 5 deletions(-) > > diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c > index 2645cfb5718b..c5da29ad010c 100644 > --- a/kernel/dma/pool.c > +++ b/kernel/dma/pool.c > @@ -184,6 +184,12 @@ static __init struct gen_pool *__dma_atomic_pool_init(size_t pool_size, > return pool; > } > > +#ifdef CONFIG_ZONE_DMA32 > +#define has_managed_dma32 has_managed_zone(ZONE_DMA32) > +#else > +#define has_managed_dma32 false > +#endif > + > static int __init dma_atomic_pool_init(void) > { > int ret = 0; > @@ -199,17 +205,20 @@ static int __init dma_atomic_pool_init(void) > } > INIT_WORK(&atomic_pool_work, atomic_pool_work_fn); > > - atomic_pool_kernel = __dma_atomic_pool_init(atomic_pool_size, > + /* All memory might be in the DMA zone(s) to begin with */ > + if (has_managed_zone(ZONE_NORMAL)) { > + atomic_pool_kernel = __dma_atomic_pool_init(atomic_pool_size, > GFP_KERNEL); > - if (!atomic_pool_kernel) > - ret = -ENOMEM; > + if (!atomic_pool_kernel) > + ret = -ENOMEM; > + } > if (has_managed_dma()) { > atomic_pool_dma = __dma_atomic_pool_init(atomic_pool_size, > GFP_KERNEL | GFP_DMA); > if (!atomic_pool_dma) > ret = -ENOMEM; > } > - if (IS_ENABLED(CONFIG_ZONE_DMA32)) { > + if (has_managed_dma32) { > atomic_pool_dma32 = __dma_atomic_pool_init(atomic_pool_size, > GFP_KERNEL | GFP_DMA32); > if (!atomic_pool_dma32) > @@ -228,7 +237,7 @@ static inline struct gen_pool *dma_guess_pool(struct gen_pool *prev, gfp_t gfp) > return atomic_pool_dma ?: atomic_pool_dma32 ?: atomic_pool_kernel; > if (gfp & GFP_DMA32) > return atomic_pool_dma32 ?: atomic_pool_dma ?: atomic_pool_kernel; > - return atomic_pool_kernel; > + return atomic_pool_kernel ?: atomic_pool_dma32 ?: atomic_pool_dma; > } > if (prev == atomic_pool_kernel) > return atomic_pool_dma32 ? atomic_pool_dma32 : atomic_pool_dma; > -- > 2.34.1 > >