linux-kernel - Re: [PATCH -next 2/3] mm/zswap: delay the initializaton of zswap until the first enablement

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Date:   Sat, 27 Aug 2022 10:01:16 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Nathan Chancellor <nathan@...nel.org>,
        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


On 2022/8/27 4:25, Nathan Chancellor wrote:
> 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>
>> ---
...
>> 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!
Thanks for your reporting，we will check it.
>
> Cheers,
> Nathan
>
> .