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Wed, 12 Nov 2025 21:10:13 -0800 (PST) Received: from google.com ([2401:fa00:8f:203:6d96:d8c6:55e6:2377]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2985c2346f3sm9713465ad.18.2025.11.12.21.10.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 12 Nov 2025 21:10:12 -0800 (PST) Date: Thu, 13 Nov 2025 14:10:07 +0900 From: Sergey Senozhatsky To: Yuwen Chen Cc: axboe@kernel.dk, akpm@linux-foundation.org, bgeffon@google.com, licayy@outlook.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, liumartin@google.com, minchan@kernel.org, richardycc@google.com, Sergey Senozhatsky Subject: Re: [PATCH v4] zram: Implement multi-page write-back Message-ID: References: <83d64478-d53c-441f-b5b4-55b5f1530a03@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 856AB180005 X-Stat-Signature: nsrgkzoa9nqi9f7rnesn1kb46fnuqhyz X-Rspamd-Server: rspam02 X-Rspam-User: X-HE-Tag: 1763010614-258272 X-HE-Meta: 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 OHYhMOsP waWkYu93h+BqjJxj8pXOJiBRozv7OSRnSkwCoki3kt2jeHNOx8AafAnH0B3kQwjrVxt+3ceT66kgfhY6ux1H9TuRu9Lm8xt/q39LZcXFK9WAZ5czIXyD/XTH2lVykxlN4UEgnZDln78qqsMfc49Mh9xp0E9vohCMIiMtfymLhhcy/C5X70OD1kzBCaU6dVU86NI2sUvxS5o4Vvt2cQBkChpvXCgnJsZAuKoZzO2nzHdObxXo8gNr9sfJMX+TelcJJI6+IJOA6NfLF/JFR05PjhdkpddW/w56K7UJ/Hb0OCNcmEQEw60HZ5y2xKgNwdALqe3laBqGcEDtaFsoa+RrBOKUKQlqu+sKXy6gx3duSCyqm6ik= 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 (25/11/13 11:04), Sergey Senozhatsky wrote: > On (25/11/06 09:49), Yuwen Chen wrote: > > + > > +#define ZRAM_WB_REQ_CNT (32) > > + > > How was this number chosen? Did you try lower/higher values? > I think we might want this to be runtime tunable via sysfs, e.g. > writeback_batch_size attr, with min value of 1. So I think something like this should work: --- drivers/block/zram/zram_drv.c | 50 ++++++++++++++++++++++++++++++----- drivers/block/zram/zram_drv.h | 1 + 2 files changed, 45 insertions(+), 6 deletions(-) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 10b6e57603a0..cf92d4e8ca9b 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -570,6 +570,44 @@ static ssize_t writeback_limit_show(struct device *dev, return sysfs_emit(buf, "%llu\n", val); } +static ssize_t writeback_batch_size_store(struct device *dev, + struct device_attribute *attr, + const char *buf, size_t len) +{ + struct zram *zram = dev_to_zram(dev); + u32 val; + ssize_t ret = -EINVAL; + + if (kstrtouint(buf, 10, &val)) + return ret; + + if (!val) + val = 1; + + down_read(&zram->init_lock); + zram->wb_batch_size = val; + up_read(&zram->init_lock); + ret = len; + + return ret; +} + +static ssize_t writeback_batch_size_show(struct device *dev, + struct device_attribute *attr, + char *buf) +{ + u32 val; + struct zram *zram = dev_to_zram(dev); + + down_read(&zram->init_lock); + spin_lock(&zram->wb_limit_lock); + val = zram->wb_batch_size; + spin_unlock(&zram->wb_limit_lock); + up_read(&zram->init_lock); + + return sysfs_emit(buf, "%u\n", val); +} + static void reset_bdev(struct zram *zram) { if (!zram->backing_dev) @@ -776,10 +814,7 @@ static void release_wb_ctl(struct zram_wb_ctl *wb_ctl) kfree(wb_ctl); } -/* should be a module param */ -#define ZRAM_WB_REQ_CNT (32) - -static struct zram_wb_ctl *init_wb_ctl(void) +static struct zram_wb_ctl *init_wb_ctl(struct zram *zram) { struct zram_wb_ctl *wb_ctl; int i; @@ -793,7 +828,7 @@ static struct zram_wb_ctl *init_wb_ctl(void) atomic_set(&wb_ctl->num_inflight, 0); init_completion(&wb_ctl->done); - for (i = 0; i < ZRAM_WB_REQ_CNT; i++) { + for (i = 0; i < zram->wb_batch_size; i++) { struct zram_wb_req *req; req = kmalloc(sizeof(*req), GFP_KERNEL); @@ -1145,7 +1180,7 @@ static ssize_t writeback_store(struct device *dev, goto release_init_lock; } - wb_ctl = init_wb_ctl(); + wb_ctl = init_wb_ctl(zram); if (!wb_ctl) { ret = -ENOMEM; goto release_init_lock; @@ -2786,6 +2821,7 @@ static DEVICE_ATTR_RW(backing_dev); static DEVICE_ATTR_WO(writeback); static DEVICE_ATTR_RW(writeback_limit); static DEVICE_ATTR_RW(writeback_limit_enable); +static DEVICE_ATTR_RW(writeback_batch_size); #endif #ifdef CONFIG_ZRAM_MULTI_COMP static DEVICE_ATTR_RW(recomp_algorithm); @@ -2807,6 +2843,7 @@ static struct attribute *zram_disk_attrs[] = { &dev_attr_writeback.attr, &dev_attr_writeback_limit.attr, &dev_attr_writeback_limit_enable.attr, + &dev_attr_writeback_batch_size.attr, #endif &dev_attr_io_stat.attr, &dev_attr_mm_stat.attr, @@ -2868,6 +2905,7 @@ static int zram_add(void) init_rwsem(&zram->init_lock); #ifdef CONFIG_ZRAM_WRITEBACK + zram->wb_batch_size = 1; spin_lock_init(&zram->wb_limit_lock); #endif diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h index 6cee93f9c0d0..1a647f42c1a4 100644 --- a/drivers/block/zram/zram_drv.h +++ b/drivers/block/zram/zram_drv.h @@ -129,6 +129,7 @@ struct zram { struct file *backing_dev; spinlock_t wb_limit_lock; bool wb_limit_enable; + u32 wb_batch_size; u64 bd_wb_limit; struct block_device *bdev; unsigned long *bitmap; -- 2.51.2.1041.gc1ab5b90ca-goog