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Tue, 28 Oct 2025 12:56:40 -0700 (PDT) MIME-Version: 1.0 References: <20251028034308.929550-1-bhe@redhat.com> <20251028034308.929550-3-bhe@redhat.com> In-Reply-To: <20251028034308.929550-3-bhe@redhat.com> From: Nhat Pham Date: Tue, 28 Oct 2025 12:56:28 -0700 X-Gm-Features: AWmQ_bmOuBXACtD1EpZ1FFWt5uI8t6B14R06sXXZZmSea8TeOEwh8DbHgD1FFPU Message-ID: Subject: Re: [PATCH v5 mm-new 2/2] mm/swap: select swap device with default priority round robin To: Baoquan He Cc: linux-mm@kvack.org, akpm@linux-foundation.org, chrisl@kernel.org, youngjun.park@lge.com, kasong@tencent.com, baohua@kernel.org, shikemeng@huaweicloud.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam05 X-Stat-Signature: 9x4ejwtf74defqgyarufniibf5q771s1 X-Rspam-User: X-Rspamd-Queue-Id: 00648C000A X-HE-Tag: 1761681401-165604 X-HE-Meta: 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 yOslOjtf tvABZkUp88HMtx2v18iFFPs6lNxYafwG27vk5V7HF8egLItZ5p/X0kmVXmhjx9gx/1dgCCQoT9cSfDuuD/4WFZtj0DewrYRCC2kUnFAfStz8XRcW1qz/4jVDAyOInJkc9xPb8AvL2q68Ltfx2BbBXkCBjRh6KGR5mmeX/efSGN89XJyLSren65JLS3Xs+gEAvV73zXkMSx7z+lvkg/BYyhKagnm6at6tIkIykQLFLVlan9rAVXB4C7ZCU1HvZ38lCQYyaeV9QC1uPgPMlocT+SmpxovdPAI01RVO8FC72w66639wmuqg6p+2ap3dDApzl6l3FmwFf75TEhtHbdJfCNhstqGRECh6VGyZ1po+FeFvwwiwiv1jkN14/eyLOhEI+N6jnPPbFjAZJNqFzj24egphJPMoyXCkMiDnvE1f8dwMk3lI= 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 Mon, Oct 27, 2025 at 8:43=E2=80=AFPM Baoquan He wrote: > > Swap devices are assumed to have similar accessing speed when swapon > if no priority is specified. It's unfair and doesn't make sense just > because one swap device is swapped on firstly, its priority will be > higher than the one swapped on later. > > Here, set all swap devicess to have priority '-1' by default. With this > change, swap device with default priority will be selected round robin > when swapping out. This can improve the swapping efficiency a lot among > multiple swap devices with default priority. Yeah, I agree. In a set up with multiple swap devices, this can spread out the swap writes, potentially improving throughput. > > Below are swapon output during the processes when high pressure vm-scabil= ity > test is being taken: > > 1) This is pre-commit a2468cc9bfdf, swap device is selectd one by one by > priority from high to low when one swap device is exhausted: > ------------------------------------ > [root@hp-dl385g10-03 ~]# swapon > NAME TYPE SIZE USED PRIO > /dev/zram0 partition 16G 16G -1 > /dev/zram1 partition 16G 966.2M -2 > /dev/zram2 partition 16G 0B -3 > /dev/zram3 partition 16G 0B -4 > > 2) This is behaviour with commit a2468cc9bfdf, on node, swap device > sharing the same node id is selected firstly until exhausted; while > on node no swap device sharing the node id it selects the one with > highest priority until exhaustd: > ------------------------------------ > [root@hp-dl385g10-03 ~]# swapon > NAME TYPE SIZE USED PRIO > /dev/zram0 partition 16G 15.7G -2 > /dev/zram1 partition 16G 3.4G -3 > /dev/zram2 partition 16G 3.4G -4 > /dev/zram3 partition 16G 2.6G -5 > > 3) After this patch applied, swap devices with default priority are selec= td > round robin: > ------------------------------------ > [root@hp-dl385g10-03 block]# swapon > NAME TYPE SIZE USED PRIO > /dev/zram0 partition 16G 6.6G -1 > /dev/zram1 partition 16G 6.6G -1 > /dev/zram2 partition 16G 6.6G -1 > /dev/zram3 partition 16G 6.6G -1 > > With the change, about 18% efficiency promotion relative to node based > way as below. (Surely, the pre-commit a2468cc9bfdf way is the worst.) > > vm-scability test: > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > Test with: > usemem --init-time -O -y -x -n 31 2G (4G memcg, zram as swap) > one by one: node based: round robin= : > System time: 1087.38 s 637.92 s 526.74 s = (lower is better) > Sum Throughput: 2036.55 MB/s 3546.56 MB/s 4207.56 MB/= s (higher is better) > Single process Throughput: 65.69 MB/s 114.40 MB/s 135.72 MB/s= (high is better) > free latency: 15769409.48 us 10138455.99 us 6810119.01 = us(lower is better) > > Suggested-by: Chris Li > Acked-by: Chris Li > Signed-off-by: Baoquan He Acked-by: Nhat Pham