Re: [PATCH v6 1/4] mm/slub: enable debugging memory wasting of kmalloc

From: Vlastimil Babka
Date: Sun Oct 30 2022 - 17:31:02 EST

On 10/30/22 20:23, John Thomson wrote:
On Tue, 13 Sep 2022, at 06:54, Feng Tang wrote:
kmalloc's API family is critical for mm, with one nature that it will
round up the request size to a fixed one (mostly power of 2). Say
when user requests memory for '2^n + 1' bytes, actually 2^(n+1) bytes
could be allocated, so in worst case, there is around 50% memory
space waste.


I have a ralink mt7621 router running Openwrt, using the mips ZBOOT kernel, and appear to have bisected
a very-nearly-clean kernel v6.1rc-2 boot issue to this commit.
I have 3 commits atop 6.1-rc2: fix a ZBOOT compile error, use the Openwrt LZMA options,
and enable DEBUG_ZBOOT for my platform. I am compiling my kernel within the Openwrt build system.
No guarantees this is not due to something I am doing wrong, but any insight would be greatly appreciated.


On UART, No indication of the (once extracted) kernel booting:

transfer started ......................................... transfer ok, time=2.01s
setting up elf image... OK
jumping to kernel code
zimage at: 80BA4100 810D4720
Uncompressing Linux at load address 80001000
Copy device tree to address 80B96EE0
Now, booting the kernel...

It's weird that the commit would cause no output so early, SLUB code is run only later.

Nothing follows

6edf2576a6cc ("mm/slub: enable debugging memory wasting of kmalloc") reverted, normal boot:
transfer started ......................................... transfer ok, time=2.01s
setting up elf image... OK
jumping to kernel code
zimage at: 80BA4100 810D47A4
Uncompressing Linux at load address 80001000
Copy device tree to address 80B96EE0
Now, booting the kernel...

[ 0.000000] Linux version 6.1.0-rc2 (john@john) (mipsel-openwrt-linux-musl-gcc (OpenWrt GCC 11.3.0 r19724+16-1521d5f453) 11.3.0, GNU ld (GNU Binutils) 2.37) #0 SMP Fri Oct 28 03:48:10 2022
[ 0.000000] SoC Type: MediaTek MT7621 ver:1 eco:3
[ 0.000000] printk: bootconsole [early0] enabled
[ 0.000000] CPU0 revision is: 0001992f (MIPS 1004Kc)
[ 0.000000] MIPS: machine is MikroTik RouterBOARD 760iGS
[ 0.000000] Initrd not found or empty - disabling initrd
[ 0.000000] VPE topology {2,2} total 4
[ 0.000000] Primary instruction cache 32kB, VIPT, 4-way, linesize 32 bytes.
[ 0.000000] Primary data cache 32kB, 4-way, PIPT, no aliases, linesize 32 bytes
[ 0.000000] MIPS secondary cache 256kB, 8-way, linesize 32 bytes.
[ 0.000000] Zone ranges:
[ 0.000000] Normal [mem 0x0000000000000000-0x000000000fffffff]
[ 0.000000] HighMem empty
[ 0.000000] Movable zone start for each node
[ 0.000000] Early memory node ranges
[ 0.000000] node 0: [mem 0x0000000000000000-0x000000000fffffff]
[ 0.000000] Initmem setup node 0 [mem 0x0000000000000000-0x000000000fffffff]
[ 0.000000] percpu: Embedded 11 pages/cpu s16064 r8192 d20800 u45056
[ 0.000000] Built 1 zonelists, mobility grouping on. Total pages: 64960
[ 0.000000] Kernel command line: console=ttyS0,115200 rootfstype=squashfs,jffs2
[ 0.000000] Dentry cache hash table entries: 32768 (order: 5, 131072 bytes, linear)
[ 0.000000] Inode-cache hash table entries: 16384 (order: 4, 65536 bytes, linear)
[ 0.000000] Writing ErrCtl register=00019146
[ 0.000000] Readback ErrCtl register=00019146
[ 0.000000] mem auto-init: stack:off, heap alloc:off, heap free:off
[ 0.000000] Memory: 246220K/262144K available (7455K kernel code, 628K rwdata, 1308K rodata, 3524K init, 245K bss, 15924K reserved, 0K cma-reserved, 0K highmem)
[ 0.000000] SLUB: HWalign=32, Order=0-3, MinObjects=0, CPUs=4, Nodes=1
[ 0.000000] rcu: Hierarchical RCU implementation.


boot continues as expected


possibly relevant config options:
grep -E '(SLUB|SLAB)' .config
# SLAB allocator options
# CONFIG_SLAB is not set
CONFIG_SLUB=y
CONFIG_SLAB_MERGE_DEFAULT=y
# CONFIG_SLAB_FREELIST_RANDOM is not set
# CONFIG_SLAB_FREELIST_HARDENED is not set
# CONFIG_SLUB_STATS is not set
CONFIG_SLUB_CPU_PARTIAL=y
# end of SLAB allocator options
# CONFIG_SLUB_DEBUG is not set

Also not having CONFIG_SLUB_DEBUG enabled means most of the code the patch/commit touches is not even active.
Could this be some miscompile or code layout change exposing some different bug, hmm.
Is it any different if you do enable CONFIG_SLUB_DEBUG ?
Or change to CONFIG_SLAB? (that would be really weird if not)


With this commit reverted: cpuinfo and meminfo

system type : MediaTek MT7621 ver:1 eco:3
machine : MikroTik RouterBOARD 760iGS
processor : 0
cpu model : MIPS 1004Kc V2.15
BogoMIPS : 586.13
wait instruction : yes
microsecond timers : yes
tlb_entries : 32
extra interrupt vector : yes
hardware watchpoint : yes, count: 4, address/irw mask: [0x0ffc, 0x0ffc, 0x0ffb, 0x0ffb]
isa : mips1 mips2 mips32r1 mips32r2
ASEs implemented : mips16 dsp mt
Options implemented : tlb 4kex 4k_cache prefetch mcheck ejtag llsc pindexed_dcache userlocal vint perf_cntr_intr_bit cdmm perf
shadow register sets : 1
kscratch registers : 0
package : 0
core : 0
VPE : 0
VCED exceptions : not available
VCEI exceptions : not available

processor : 1
cpu model : MIPS 1004Kc V2.15
BogoMIPS : 586.13
wait instruction : yes
microsecond timers : yes
tlb_entries : 32
extra interrupt vector : yes
hardware watchpoint : yes, count: 4, address/irw mask: [0x0ffc, 0x0ffc, 0x0ffb, 0x0ffb]
isa : mips1 mips2 mips32r1 mips32r2
ASEs implemented : mips16 dsp mt
Options implemented : tlb 4kex 4k_cache prefetch mcheck ejtag llsc pindexed_dcache userlocal vint perf_cntr_intr_bit cdmm perf
shadow register sets : 1
kscratch registers : 0
package : 0
core : 0
VPE : 1
VCED exceptions : not available
VCEI exceptions : not available

processor : 2
cpu model : MIPS 1004Kc V2.15
BogoMIPS : 586.13
wait instruction : yes
microsecond timers : yes
tlb_entries : 32
extra interrupt vector : yes
hardware watchpoint : yes, count: 4, address/irw mask: [0x0ffc, 0x0ffc, 0x0ffb, 0x0ffb]
isa : mips1 mips2 mips32r1 mips32r2
ASEs implemented : mips16 dsp mt
Options implemented : tlb 4kex 4k_cache prefetch mcheck ejtag llsc pindexed_dcache userlocal vint perf_cntr_intr_bit cdmm perf
shadow register sets : 1
kscratch registers : 0
package : 0
core : 1
VPE : 0
VCED exceptions : not available
VCEI exceptions : not available

processor : 3
cpu model : MIPS 1004Kc V2.15
BogoMIPS : 586.13
wait instruction : yes
microsecond timers : yes
tlb_entries : 32
extra interrupt vector : yes
hardware watchpoint : yes, count: 4, address/irw mask: [0x0ffc, 0x0ffc, 0x0ffb, 0x0ffb]
isa : mips1 mips2 mips32r1 mips32r2
ASEs implemented : mips16 dsp mt
Options implemented : tlb 4kex 4k_cache prefetch mcheck ejtag llsc pindexed_dcache userlocal vint perf_cntr_intr_bit cdmm perf
shadow register sets : 1
kscratch registers : 0
package : 0
core : 1
VPE : 1
VCED exceptions : not available
VCEI exceptions : not available

MemTotal: 249744 kB
MemFree: 211088 kB
MemAvailable: 187364 kB
Buffers: 0 kB
Cached: 8824 kB
SwapCached: 0 kB
Active: 1104 kB
Inactive: 8860 kB
Active(anon): 1104 kB
Inactive(anon): 8860 kB
Active(file): 0 kB
Inactive(file): 0 kB
Unevictable: 0 kB
Mlocked: 0 kB
HighTotal: 0 kB
HighFree: 0 kB
LowTotal: 249744 kB
LowFree: 211088 kB
SwapTotal: 0 kB
SwapFree: 0 kB
Dirty: 0 kB
Writeback: 0 kB
AnonPages: 1192 kB
Mapped: 2092 kB
Shmem: 8824 kB
KReclaimable: 1704 kB
Slab: 9372 kB
SReclaimable: 1704 kB
SUnreclaim: 7668 kB
KernelStack: 592 kB
PageTables: 264 kB
SecPageTables: 0 kB
NFS_Unstable: 0 kB
Bounce: 0 kB
WritebackTmp: 0 kB
CommitLimit: 124872 kB
Committed_AS: 14676 kB
VmallocTotal: 1040376 kB
VmallocUsed: 2652 kB
VmallocChunk: 0 kB
Percpu: 272 kB


Cheers,