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Message-ID: <YwksRZPIfXmlOmHR@dev-arch.thelio-3990X>
Date: Fri, 26 Aug 2022 13:25:41 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Liu Shixin <liushixin2@...wei.com>
Cc: Seth Jennings <sjenning@...hat.com>,
Dan Streetman <ddstreet@...e.org>,
Vitaly Wool <vitaly.wool@...sulko.com>,
Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next 2/3] mm/zswap: delay the initializaton of zswap
until the first enablement
Hi Liu,
On Thu, Aug 25, 2022 at 10:20:36PM +0800, Liu Shixin wrote:
> In the initialization of zswap, about 18MB memory will be allocated for
> zswap_pool in my machine. Since not all users use zswap, the memory may be
> wasted. Save the memory for these users by delaying the initialization of
> zswap to first enablement.
>
> Signed-off-by: Liu Shixin <liushixin2@...wei.com>
> ---
> mm/zswap.c | 48 +++++++++++++++++++++++++++++++++++++++---------
> 1 file changed, 39 insertions(+), 9 deletions(-)
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 84e38300f571..90df72aceb08 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -81,6 +81,8 @@ static bool zswap_pool_reached_full;
>
> #define ZSWAP_PARAM_UNSET ""
>
> +static int zswap_setup(void);
> +
> /* Enable/disable zswap */
> static bool zswap_enabled = IS_ENABLED(CONFIG_ZSWAP_DEFAULT_ON);
> static int zswap_enabled_param_set(const char *,
> @@ -220,6 +222,8 @@ static atomic_t zswap_pools_count = ATOMIC_INIT(0);
>
> /* init state */
> static int zswap_init_state;
> +/* used to ensure the integrity of initialization */
> +static DEFINE_MUTEX(zswap_init_lock);
>
> /* init completed, but couldn't create the initial pool */
> static bool zswap_has_pool;
> @@ -273,13 +277,13 @@ static void zswap_update_total_size(void)
> **********************************/
> static struct kmem_cache *zswap_entry_cache;
>
> -static int __init zswap_entry_cache_create(void)
> +static int zswap_entry_cache_create(void)
> {
> zswap_entry_cache = KMEM_CACHE(zswap_entry, 0);
> return zswap_entry_cache == NULL;
> }
>
> -static void __init zswap_entry_cache_destroy(void)
> +static void zswap_entry_cache_destroy(void)
> {
> kmem_cache_destroy(zswap_entry_cache);
> }
> @@ -664,7 +668,7 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor)
> return NULL;
> }
>
> -static __init struct zswap_pool *__zswap_pool_create_fallback(void)
> +static struct zswap_pool *__zswap_pool_create_fallback(void)
> {
> bool has_comp, has_zpool;
>
> @@ -782,11 +786,17 @@ static int __zswap_param_set(const char *val, const struct kernel_param *kp,
> if (!strcmp(s, *(char **)kp->arg) && zswap_has_pool)
> return 0;
>
> - /* if this is load-time (pre-init) param setting,
> + /*
> + * if zswap has not been initialized,
> * don't create a pool; that's done during init.
> */
> - if (zswap_init_state == ZSWAP_UNINIT)
> - return param_set_charp(s, kp);
> + mutex_lock(&zswap_init_lock);
> + if (zswap_init_state == ZSWAP_UNINIT) {
> + ret = param_set_charp(s, kp);
> + mutex_unlock(&zswap_init_lock);
> + return ret;
> + }
> + mutex_unlock(&zswap_init_lock);
>
> if (!type) {
> if (!zpool_has_pool(s)) {
> @@ -876,6 +886,14 @@ static int zswap_zpool_param_set(const char *val,
> static int zswap_enabled_param_set(const char *val,
> const struct kernel_param *kp)
> {
> + if (system_state == SYSTEM_RUNNING) {
> + mutex_lock(&zswap_init_lock);
> + if (zswap_setup()) {
> + mutex_unlock(&zswap_init_lock);
> + return -ENODEV;
> + }
> + mutex_unlock(&zswap_init_lock);
> + }
> if (zswap_init_state == ZSWAP_INIT_FAILED) {
> pr_err("can't enable, initialization failed\n");
> return -ENODEV;
> @@ -1432,7 +1450,7 @@ static const struct frontswap_ops zswap_frontswap_ops = {
>
> static struct dentry *zswap_debugfs_root;
>
> -static int __init zswap_debugfs_init(void)
> +static int zswap_debugfs_init(void)
> {
> if (!debugfs_initialized())
> return -ENODEV;
> @@ -1463,7 +1481,7 @@ static int __init zswap_debugfs_init(void)
> return 0;
> }
> #else
> -static int __init zswap_debugfs_init(void)
> +static int zswap_debugfs_init(void)
> {
> return 0;
> }
> @@ -1472,11 +1490,14 @@ static int __init zswap_debugfs_init(void)
> /*********************************
> * module init and exit
> **********************************/
> -static int __init init_zswap(void)
> +static int zswap_setup(void)
> {
> struct zswap_pool *pool;
> int ret;
>
> + if (zswap_init_state != ZSWAP_UNINIT)
> + return 0;
> +
> if (zswap_entry_cache_create()) {
> pr_err("entry cache creation failed\n");
> goto cache_fail;
> @@ -1534,6 +1555,15 @@ static int __init init_zswap(void)
> zswap_enabled = false;
> return -ENOMEM;
> }
> +
> +static int __init init_zswap(void)
> +{
> + /* skip init if zswap is disabled when system startup */
> + if (!zswap_enabled)
> + return 0;
> + return zswap_setup();
> +}
> +
> /* must be late so crypto has time to come up */
> late_initcall(init_zswap);
>
> --
> 2.25.1
>
>
This change is in -next as commit 22100432cf14 ("mm/zswap: delay the
initializaton of zswap until the first enablement"). I just bisected my
arm64 test system running Fedora failing to boot due to that commit,
with the following stack trace:
Unable to handle kernel access to user memory outside uaccess routines at virtual address 0000000000000000
Mem abort info:
ESR = 0x0000000096000004
EC = 0x25: DABT (current EL), IL = 32 bits
SET = 0, FnV = 0
EA = 0, S1PTW = 0
FSC = 0x04: level 0 translation fault
Data abort info:
ISV = 0, ISS = 0x00000004
CM = 0, WnR = 0
user pgtable: 4k pages, 48-bit VAs, pgdp=00000020a4fab000
[0000000000000000] pgd=0000000000000000, p4d=0000000000000000
Internal error: Oops: 96000004 [#1] SMP
Modules linked in: zram fsl_dpaa2_eth pcs_lynx phylink ahci_qoriq crct10dif_ce ghash_ce sbsa_gwdt fsl_mc_dpio nvme lm90 nvme_core at803x xhci_plat_hcd rtc_fsl_ftm_alarm xgmac_mdio ahci_platform i2c_imx ip6_tables ip_tables fuse
Unloaded tainted modules: cppc_cpufreq():1
CPU: 10 PID: 761 Comm: swapon Not tainted 6.0.0-rc2-00454-g22100432cf14 #1
Hardware name: SolidRun Ltd. SolidRun CEX7 Platform, BIOS EDK II Jun 21 2022
pstate: 00400005 (nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : frontswap_init+0x38/0x60
lr : __do_sys_swapon+0x8a8/0x9f4
sp : ffff80000969bcf0
x29: ffff80000969bcf0 x28: ffff37bee0d8fc00 x27: ffff80000a7f5000
x26: fffffcdefb971e80 x25: ffffaba797453b90 x24: 0000000000000064
x23: ffff37c1f209d1a8 x22: ffff37bee880e000 x21: ffffaba797748560
x20: ffff37bee0d8fce4 x19: ffffaba797748488 x18: 0000000000000014
x17: 0000000030ec029a x16: ffffaba795a479b0 x15: 0000000000000000
x14: 0000000000000000 x13: 0000000000000030 x12: 0000000000000001
x11: ffff37c63c0aba18 x10: 0000000000000000 x9 : ffffaba7956b8c88
x8 : ffff80000969bcd0 x7 : 0000000000000000 x6 : 0000000000000000
x5 : 0000000000000001 x4 : 0000000000000000 x3 : ffffaba79730f000
x2 : ffff37bee0d8fc00 x1 : 0000000000000000 x0 : 0000000000000000
Call trace:
frontswap_init+0x38/0x60
__do_sys_swapon+0x8a8/0x9f4
__arm64_sys_swapon+0x28/0x3c
invoke_syscall+0x78/0x100
el0_svc_common.constprop.0+0xd4/0xf4
do_el0_svc+0x38/0x4c
el0_svc+0x34/0x10c
el0t_64_sync_handler+0x11c/0x150
el0t_64_sync+0x190/0x194
Code: d000e283 910003fd f9006c41 f946d461 (f9400021)
---[ end trace 0000000000000000 ]---
This is with Fedora's configuration:
https://src.fedoraproject.org/rpms/kernel/raw/rawhide/f/kernel-aarch64-fedora.config
If there is any more information I can provide or patches I can test, I
am more than happy to do so!
Cheers,
Nathan
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