Re: [PATCH 2/2] kcompressd: Add Kcompressd for accelerated zram compression
From: Qun-wei Lin (林群崴)
Date: Mon Mar 10 2025 - 09:26:54 EST
On Sat, 2025-03-08 at 08:41 +1300, Barry Song wrote:
>
> External email : Please do not click links or open attachments until
> you have verified the sender or the content.
>
>
> On Sat, Mar 8, 2025 at 1:02 AM Qun-Wei Lin <qun-wei.lin@xxxxxxxxxxxx>
> wrote:
> >
> > Introduced Kcompressd to offload zram page compression, improving
> > system efficiency by handling compression separately from memory
> > reclaiming. Added necessary configurations and dependencies.
> >
> > Signed-off-by: Qun-Wei Lin <qun-wei.lin@xxxxxxxxxxxx>
> > ---
> > drivers/block/zram/Kconfig | 11 ++
> > drivers/block/zram/Makefile | 3 +-
> > drivers/block/zram/kcompressd.c | 340
> > ++++++++++++++++++++++++++++++++
> > drivers/block/zram/kcompressd.h | 25 +++
> > drivers/block/zram/zram_drv.c | 22 ++-
> > 5 files changed, 397 insertions(+), 4 deletions(-)
> > create mode 100644 drivers/block/zram/kcompressd.c
> > create mode 100644 drivers/block/zram/kcompressd.h
> >
> > diff --git a/drivers/block/zram/Kconfig
> > b/drivers/block/zram/Kconfig
> > index 402b7b175863..f0a1b574f770 100644
> > --- a/drivers/block/zram/Kconfig
> > +++ b/drivers/block/zram/Kconfig
> > @@ -145,3 +145,14 @@ config ZRAM_MULTI_COMP
> > re-compress pages using a potentially slower but more
> > effective
> > compression algorithm. Note, that IDLE page recompression
> > requires ZRAM_TRACK_ENTRY_ACTIME.
> > +
> > +config KCOMPRESSD
> > + tristate "Kcompressd: Accelerated zram compression"
> > + depends on ZRAM
> > + help
> > + Kcompressd creates multiple daemons to accelerate the
> > compression of pages
> > + in zram, offloading this time-consuming task from the
> > zram driver.
> > +
> > + This approach improves system efficiency by handling page
> > compression separately,
> > + which was originally done by kswapd or direct reclaim.
>
> For direct reclaim, we were previously able to compress using
> multiple CPUs
> with multi-threading.
> After your patch, it seems that only a single thread/CPU is used for
> compression
> so it won't necessarily improve direct reclaim performance?
>
Our patch only splits the context of kswapd. When direct reclaim is
occurred, it is bypassed, so direct reclaim remains unchanged, with
each thread that needs memory directly reclaiming it.
> Even for kswapd, we used to have multiple threads like [kswapd0],
> [kswapd1],
> and [kswapd2] for different nodes. Now, are we also limited to just
> one thread?
We only considered a single kswapd here and didn't account for multiple
instances. Since I use kfifo to collect the bios, if there are multiple
kswapds, we need to add a lock to protect the bio queue. I can revise
this in the 2nd version, or do you have any other suggested approaches?
> I also wonder if this could be handled at the vmscan level instead of
> the zram
> level. then it might potentially help other sync devices or even
> zswap later.
>
> But I agree that for phones, modifying zram seems like an easier
> starting
> point. However, relying on a single thread isn't always the best
> approach.
>
>
> > +
> > diff --git a/drivers/block/zram/Makefile
> > b/drivers/block/zram/Makefile
> > index 0fdefd576691..23baa5dfceb9 100644
> > --- a/drivers/block/zram/Makefile
> > +++ b/drivers/block/zram/Makefile
> > @@ -9,4 +9,5 @@ zram-$(CONFIG_ZRAM_BACKEND_ZSTD) +=
> > backend_zstd.o
> > zram-$(CONFIG_ZRAM_BACKEND_DEFLATE) += backend_deflate.o
> > zram-$(CONFIG_ZRAM_BACKEND_842) += backend_842.o
> >
> > -obj-$(CONFIG_ZRAM) += zram.o
> > +obj-$(CONFIG_ZRAM) += zram.o
> > +obj-$(CONFIG_KCOMPRESSD) += kcompressd.o
> > diff --git a/drivers/block/zram/kcompressd.c
> > b/drivers/block/zram/kcompressd.c
> > new file mode 100644
> > index 000000000000..195b7e386869
> > --- /dev/null
> > +++ b/drivers/block/zram/kcompressd.c
> > @@ -0,0 +1,340 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright (C) 2024 MediaTek Inc.
> > + */
> > +
> > +#include <linux/module.h>
> > +#include <linux/kernel.h>
> > +#include <linux/bio.h>
> > +#include <linux/bitops.h>
> > +#include <linux/freezer.h>
> > +#include <linux/kernel.h>
> > +#include <linux/psi.h>
> > +#include <linux/kfifo.h>
> > +#include <linux/swap.h>
> > +#include <linux/delay.h>
> > +
> > +#include "kcompressd.h"
> > +
> > +#define INIT_QUEUE_SIZE 4096
> > +#define DEFAULT_NR_KCOMPRESSD 4
> > +
> > +static atomic_t enable_kcompressd;
> > +static unsigned int nr_kcompressd;
> > +static unsigned int queue_size_per_kcompressd;
> > +static struct kcompress *kcompress;
> > +
> > +enum run_state {
> > + KCOMPRESSD_NOT_STARTED = 0,
> > + KCOMPRESSD_RUNNING,
> > + KCOMPRESSD_SLEEPING,
> > +};
> > +
> > +struct kcompressd_para {
> > + wait_queue_head_t *kcompressd_wait;
> > + struct kfifo *write_fifo;
> > + atomic_t *running;
> > +};
> > +
> > +static struct kcompressd_para *kcompressd_para;
> > +static BLOCKING_NOTIFIER_HEAD(kcompressd_notifier_list);
> > +
> > +struct write_work {
> > + void *mem;
> > + struct bio *bio;
> > + compress_callback cb;
> > +};
> > +
> > +int kcompressd_enabled(void)
> > +{
> > + return likely(atomic_read(&enable_kcompressd));
> > +}
> > +EXPORT_SYMBOL(kcompressd_enabled);
> > +
> > +static void kcompressd_try_to_sleep(struct kcompressd_para *p)
> > +{
> > + DEFINE_WAIT(wait);
> > +
> > + if (!kfifo_is_empty(p->write_fifo))
> > + return;
> > +
> > + if (freezing(current) || kthread_should_stop())
> > + return;
> > +
> > + atomic_set(p->running, KCOMPRESSD_SLEEPING);
> > + prepare_to_wait(p->kcompressd_wait, &wait,
> > TASK_INTERRUPTIBLE);
> > +
> > + /*
> > + * After a short sleep, check if it was a premature sleep.
> > If not, then
> > + * go fully to sleep until explicitly woken up.
> > + */
> > + if (!kthread_should_stop() && kfifo_is_empty(p-
> > >write_fifo))
> > + schedule();
> > +
> > + finish_wait(p->kcompressd_wait, &wait);
> > + atomic_set(p->running, KCOMPRESSD_RUNNING);
> > +}
> > +
> > +static int kcompressd(void *para)
> > +{
> > + struct task_struct *tsk = current;
> > + struct kcompressd_para *p = (struct kcompressd_para *)para;
> > +
> > + tsk->flags |= PF_MEMALLOC | PF_KSWAPD;
> > + set_freezable();
> > +
> > + while (!kthread_should_stop()) {
> > + bool ret;
> > +
> > + kcompressd_try_to_sleep(p);
> > + ret = try_to_freeze();
> > + if (kthread_should_stop())
> > + break;
> > +
> > + if (ret)
> > + continue;
> > +
> > + while (!kfifo_is_empty(p->write_fifo)) {
> > + struct write_work entry;
> > +
> > + if (sizeof(struct write_work) ==
> > kfifo_out(p->write_fifo,
> > + &entry,
> > sizeof(struct write_work))) {
> > + entry.cb(entry.mem, entry.bio);
> > + bio_put(entry.bio);
> > + }
> > + }
> > +
> > + }
> > +
> > + tsk->flags &= ~(PF_MEMALLOC | PF_KSWAPD);
> > + atomic_set(p->running, KCOMPRESSD_NOT_STARTED);
> > + return 0;
> > +}
> > +
> > +static int init_write_queue(void)
> > +{
> > + int i;
> > + unsigned int queue_len = queue_size_per_kcompressd *
> > sizeof(struct write_work);
> > +
> > + for (i = 0; i < nr_kcompressd; i++) {
> > + if (kfifo_alloc(&kcompress[i].write_fifo,
> > + queue_len, GFP_KERNEL)) {
> > + pr_err("Failed to alloc kfifo %d\n", i);
> > + return -ENOMEM;
> > + }
> > + }
> > + return 0;
> > +}
> > +
> > +static void clean_bio_queue(int idx)
> > +{
> > + struct write_work entry;
> > +
> > + while (sizeof(struct write_work) ==
> > kfifo_out(&kcompress[idx].write_fifo,
> > + &entry, sizeof(struct write_work)))
> > {
> > + bio_put(entry.bio);
> > + entry.cb(entry.mem, entry.bio);
> > + }
> > + kfifo_free(&kcompress[idx].write_fifo);
> > +}
> > +
> > +static int kcompress_update(void)
> > +{
> > + int i;
> > + int ret;
> > +
> > + kcompress = kvmalloc_array(nr_kcompressd, sizeof(struct
> > kcompress), GFP_KERNEL);
> > + if (!kcompress)
> > + return -ENOMEM;
> > +
> > + kcompressd_para = kvmalloc_array(nr_kcompressd,
> > sizeof(struct kcompressd_para), GFP_KERNEL);
> > + if (!kcompressd_para)
> > + return -ENOMEM;
> > +
> > + ret = init_write_queue();
> > + if (ret) {
> > + pr_err("Initialization of writing to FIFOs
> > failed!!\n");
> > + return ret;
> > + }
> > +
> > + for (i = 0; i < nr_kcompressd; i++) {
> > + init_waitqueue_head(&kcompress[i].kcompressd_wait);
> > + kcompressd_para[i].kcompressd_wait =
> > &kcompress[i].kcompressd_wait;
> > + kcompressd_para[i].write_fifo =
> > &kcompress[i].write_fifo;
> > + kcompressd_para[i].running = &kcompress[i].running;
> > + }
> > +
> > + return 0;
> > +}
> > +
> > +static void stop_all_kcompressd_thread(void)
> > +{
> > + int i;
> > +
> > + for (i = 0; i < nr_kcompressd; i++) {
> > + kthread_stop(kcompress[i].kcompressd);
> > + kcompress[i].kcompressd = NULL;
> > + clean_bio_queue(i);
> > + }
> > +}
> > +
> > +static int do_nr_kcompressd_handler(const char *val,
> > + const struct kernel_param *kp)
> > +{
> > + int ret;
> > +
> > + atomic_set(&enable_kcompressd, false);
> > +
> > + stop_all_kcompressd_thread();
> > +
> > + ret = param_set_int(val, kp);
> > + if (!ret) {
> > + pr_err("Invalid number of kcompressd.\n");
> > + return -EINVAL;
> > + }
> > +
> > + ret = init_write_queue();
> > + if (ret) {
> > + pr_err("Initialization of writing to FIFOs
> > failed!!\n");
> > + return ret;
> > + }
> > +
> > + atomic_set(&enable_kcompressd, true);
> > +
> > + return 0;
> > +}
> > +
> > +static const struct kernel_param_ops
> > param_ops_change_nr_kcompressd = {
> > + .set = &do_nr_kcompressd_handler,
> > + .get = ¶m_get_uint,
> > + .free = NULL,
> > +};
> > +
> > +module_param_cb(nr_kcompressd, ¶m_ops_change_nr_kcompressd,
> > + &nr_kcompressd, 0644);
> > +MODULE_PARM_DESC(nr_kcompressd, "Number of pre-created daemon for
> > page compression");
> > +
> > +static int do_queue_size_per_kcompressd_handler(const char *val,
> > + const struct kernel_param *kp)
> > +{
> > + int ret;
> > +
> > + atomic_set(&enable_kcompressd, false);
> > +
> > + stop_all_kcompressd_thread();
> > +
> > + ret = param_set_int(val, kp);
> > + if (!ret) {
> > + pr_err("Invalid queue size for kcompressd.\n");
> > + return -EINVAL;
> > + }
> > +
> > + ret = init_write_queue();
> > + if (ret) {
> > + pr_err("Initialization of writing to FIFOs
> > failed!!\n");
> > + return ret;
> > + }
> > +
> > + pr_info("Queue size for kcompressd was changed: %d\n",
> > queue_size_per_kcompressd);
> > +
> > + atomic_set(&enable_kcompressd, true);
> > + return 0;
> > +}
> > +
> > +static const struct kernel_param_ops
> > param_ops_change_queue_size_per_kcompressd = {
> > + .set = &do_queue_size_per_kcompressd_handler,
> > + .get = ¶m_get_uint,
> > + .free = NULL,
> > +};
> > +
> > +module_param_cb(queue_size_per_kcompressd,
> > ¶m_ops_change_queue_size_per_kcompressd,
> > + &queue_size_per_kcompressd, 0644);
> > +MODULE_PARM_DESC(queue_size_per_kcompressd,
> > + "Size of queue for kcompressd");
> > +
> > +int schedule_bio_write(void *mem, struct bio *bio,
> > compress_callback cb)
> > +{
> > + int i;
> > + bool submit_success = false;
> > + size_t sz_work = sizeof(struct write_work);
> > +
> > + struct write_work entry = {
> > + .mem = mem,
> > + .bio = bio,
> > + .cb = cb
> > + };
> > +
> > + if (unlikely(!atomic_read(&enable_kcompressd)))
> > + return -EBUSY;
> > +
> > + if (!nr_kcompressd || !current_is_kswapd())
> > + return -EBUSY;
> > +
> > + bio_get(bio);
> > +
> > + for (i = 0; i < nr_kcompressd; i++) {
> > + submit_success =
> > + (kfifo_avail(&kcompress[i].write_fifo) >=
> > sz_work) &&
> > + (sz_work ==
> > kfifo_in(&kcompress[i].write_fifo, &entry, sz_work));
> > +
> > + if (submit_success) {
> > + switch (atomic_read(&kcompress[i].running))
> > {
> > + case KCOMPRESSD_NOT_STARTED:
> > + atomic_set(&kcompress[i].running,
> > KCOMPRESSD_RUNNING);
> > + kcompress[i].kcompressd =
> > kthread_run(kcompressd,
> > +
> > &kcompressd_para[i], "kcompressd:%d", i);
> > + if
> > (IS_ERR(kcompress[i].kcompressd)) {
> > +
> > atomic_set(&kcompress[i].running, KCOMPRESSD_NOT_STARTED);
> > + pr_warn("Failed to start
> > kcompressd:%d\n", i);
> > + clean_bio_queue(i);
> > + }
> > + break;
> > + case KCOMPRESSD_RUNNING:
> > + break;
> > + case KCOMPRESSD_SLEEPING:
> > +
> > wake_up_interruptible(&kcompress[i].kcompressd_wait);
> > + break;
> > + }
> > + return 0;
> > + }
> > + }
> > +
> > + bio_put(bio);
> > + return -EBUSY;
> > +}
> > +EXPORT_SYMBOL(schedule_bio_write);
> > +
> > +static int __init kcompressd_init(void)
> > +{
> > + int ret;
> > +
> > + nr_kcompressd = DEFAULT_NR_KCOMPRESSD;
> > + queue_size_per_kcompressd = INIT_QUEUE_SIZE;
> > +
> > + ret = kcompress_update();
> > + if (ret) {
> > + pr_err("Init kcompressd failed!\n");
> > + return ret;
> > + }
> > +
> > + atomic_set(&enable_kcompressd, true);
> > + blocking_notifier_call_chain(&kcompressd_notifier_list, 0,
> > NULL);
> > + return 0;
> > +}
> > +
> > +static void __exit kcompressd_exit(void)
> > +{
> > + atomic_set(&enable_kcompressd, false);
> > + stop_all_kcompressd_thread();
> > +
> > + kvfree(kcompress);
> > + kvfree(kcompressd_para);
> > +}
> > +
> > +module_init(kcompressd_init);
> > +module_exit(kcompressd_exit);
> > +
> > +MODULE_LICENSE("Dual BSD/GPL");
> > +MODULE_AUTHOR("Qun-Wei Lin <qun-wei.lin@xxxxxxxxxxxx>");
> > +MODULE_DESCRIPTION("Separate the page compression from the memory
> > reclaiming");
> > +
> > diff --git a/drivers/block/zram/kcompressd.h
> > b/drivers/block/zram/kcompressd.h
> > new file mode 100644
> > index 000000000000..2fe0b424a7af
> > --- /dev/null
> > +++ b/drivers/block/zram/kcompressd.h
> > @@ -0,0 +1,25 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * Copyright (C) 2024 MediaTek Inc.
> > + */
> > +
> > +#ifndef _KCOMPRESSD_H_
> > +#define _KCOMPRESSD_H_
> > +
> > +#include <linux/rwsem.h>
> > +#include <linux/kfifo.h>
> > +#include <linux/atomic.h>
> > +
> > +typedef void (*compress_callback)(void *mem, struct bio *bio);
> > +
> > +struct kcompress {
> > + struct task_struct *kcompressd;
> > + wait_queue_head_t kcompressd_wait;
> > + struct kfifo write_fifo;
> > + atomic_t running;
> > +};
> > +
> > +int kcompressd_enabled(void);
> > +int schedule_bio_write(void *mem, struct bio *bio,
> > compress_callback cb);
> > +#endif
> > +
> > diff --git a/drivers/block/zram/zram_drv.c
> > b/drivers/block/zram/zram_drv.c
> > index 2e1a70f2f4bd..bcd63ecb6ff2 100644
> > --- a/drivers/block/zram/zram_drv.c
> > +++ b/drivers/block/zram/zram_drv.c
> > @@ -35,6 +35,7 @@
> > #include <linux/part_stat.h>
> > #include <linux/kernel_read_file.h>
> >
> > +#include "kcompressd.h"
> > #include "zram_drv.h"
> >
> > static DEFINE_IDR(zram_index_idr);
> > @@ -2240,6 +2241,15 @@ static void zram_bio_write(struct zram
> > *zram, struct bio *bio)
> > bio_endio(bio);
> > }
> >
> > +#if IS_ENABLED(CONFIG_KCOMPRESSD)
> > +static void zram_bio_write_callback(void *mem, struct bio *bio)
> > +{
> > + struct zram *zram = (struct zram *)mem;
> > +
> > + zram_bio_write(zram, bio);
> > +}
> > +#endif
> > +
> > /*
> > * Handler function for all zram I/O requests.
> > */
> > @@ -2252,6 +2262,10 @@ static void zram_submit_bio(struct bio *bio)
> > zram_bio_read(zram, bio);
> > break;
> > case REQ_OP_WRITE:
> > +#if IS_ENABLED(CONFIG_KCOMPRESSD)
> > + if (kcompressd_enabled() &&
> > !schedule_bio_write(zram, bio, zram_bio_write_callback))
> > + break;
> > +#endif
> > zram_bio_write(zram, bio);
> > break;
> > case REQ_OP_DISCARD:
> > @@ -2535,9 +2549,11 @@ static int zram_add(void)
> > #if ZRAM_LOGICAL_BLOCK_SIZE == PAGE_SIZE
> > .max_write_zeroes_sectors = UINT_MAX,
> > #endif
> > - .features =
> > BLK_FEAT_STABLE_WRITES |
> > -
> > BLK_FEAT_READ_SYNCHRONOUS |
> > -
> > BLK_FEAT_WRITE_SYNCHRONOUS,
> > + .features =
> > BLK_FEAT_STABLE_WRITES
> > + |
> > BLK_FEAT_READ_SYNCHRONOUS
> > +#if !IS_ENABLED(CONFIG_KCOMPRESSD)
> > + |
> > BLK_FEAT_WRITE_SYNCHRONOUS,
> > +#endif
> > };
> > struct zram *zram;
> > int ret, device_id;
> > --
> > 2.45.2
> >
>
> Thanks
> Barry