Re: kernel 5.10.x Reserves much more RAM than 5.11.0, 8 MB vs 20 MB

[Yang Shi <shy828301@gmail.com>]

On Thu, Oct 28, 2021 at 2:55 AM Joakim Tjernlund
<Joakim.Tjernlund@infinera.com> wrote:
>
> On Wed, 2021-10-27 at 10:12 -0700, Yang Shi wrote:
> > On Wed, Oct 27, 2021 at 5:48 AM Joakim Tjernlund
> > <Joakim.Tjernlund@infinera.com> wrote:
> > >
> > > Using a fairly minimal kernel I get a big difference in Reserved memory, using:
> > >     qemu-system-aarch64 -machine virt -kernel arch/arm64/boot/Image -cpu cortex-a53  -nographic -m 32M
> > >
> > > I get this:
> > > Linux version 5.11.0
> > > Memory: 24052K/32768K available (3520K kernel code, 684K rwdata, 548K rodata, 320K init, 245K bss, 8716K reserved, 0K cma-reserved)
> > >
> > > Versus:
> > >
> > > Linux version 5.10.75
> > > Memory: 11836K/32768K available (3518K kernel code, 684K rwdata, 540K rodata, 320K init, 244K bss, 20932K reserved, 0K cma-reserved)
> > >
> > > Reserving 20 MB RAM on a 32 MB is way too much, even 8Mb is a bit much for us.
> >
> > This might be caused by the new lockless printk buffer patch
> > introduced in 5.10. We noticed this spike on 5.10 kernel too. It may
> > have much more memory reserved for meta data and the total amount may
> > be as much as 3x of log_buf_len. The amount varies on different
> > platforms with different configs. I didn't dig too much into the
> > details to figure out how it gets the number.
> >
> > You could try to adjust CONFIG_LOG_BUF_SHIFT or set log_buf_len from
> > kernel commandline to limit the printk buffer size.
>
> I did try this by changing LOG_BUF_SHIFT but the resulting change was just minor.

Thanks for following up, then you may run into a different problem from us.

>
> To get some info about meminfo/zoneinfo I booted with an inird FS and got this:
>   Memory: 9576K/32768K available (3518K kernel code, 460K rwdata, 540K rodata, 320K init, 180K bss, 23192K reserved, 0K cma-reserved)
> The initrd only added some 3 MB's
> Here are meminfo/zoneinfo, not sure if they are useful though.

They don't show who the reserved memory is consumed by.

If possible you may run git bisect to figure out what commit caused
this problem.

>
>  cat /proc/meminfo
> MemTotal:          12416 kB
> MemFree:            4644 kB
> MemAvailable:       4064 kB
> Buffers:               0 kB
> Cached:             4788 kB
> SwapCached:            0 kB
> Active:             2500 kB
> Inactive:           2524 kB
> Active(anon):       2500 kB
> Inactive(anon):     2524 kB
> Active(file):          0 kB
> Inactive(file):        0 kB
> Unevictable:           0 kB
> Mlocked:               0 kB
> SwapTotal:             0 kB
> SwapFree:              0 kB
> Dirty:                 0 kB
> Writeback:             0 kB
> AnonPages:           248 kB
> Mapped:             1844 kB
> Shmem:              4788 kB
> KReclaimable:          0 kB
> Slab:               1712 kB
> SReclaimable:          0 kB
> SUnreclaim:         1712 kB
> KernelStack:         384 kB
> PageTables:           80 kB
> NFS_Unstable:          0 kB
> Bounce:                0 kB
> WritebackTmp:          0 kB
> CommitLimit:        6208 kB
> Committed_AS:       5636 kB
> VmallocTotal:   262930368 kB
> VmallocUsed:         324 kB
> VmallocChunk:          0 kB
> Percpu:               76 kB
> HardwareCorrupted:     0 kB
>
>  cat /proc/zoneinfo
> Node 0, zone   Normal
>   per-node stats
>       nr_inactive_anon 631
>       nr_active_anon 625
>       nr_inactive_file 0
>       nr_active_file 0
>       nr_unevictable 0
>       nr_slab_reclaimable 0
>       nr_slab_unreclaimable 429
>       nr_isolated_anon 0
>       nr_isolated_file 0
>       workingset_nodes 0
>       workingset_refault_anon 0
>       workingset_refault_file 0
>       workingset_activate_anon 0
>       workingset_activate_file 0
>       workingset_restore_anon 0
>       workingset_restore_file 0
>       workingset_nodereclaim 0
>       nr_anon_pages 62
>       nr_mapped    461
>       nr_file_pages 1197
>       nr_dirty     0
>       nr_writeback 0
>       nr_writeback_temp 0
>       nr_shmem     1197
>       nr_shmem_hugepages 0
>       nr_shmem_pmdmapped 0
>       nr_file_hugepages 0
>       nr_file_pmdmapped 0
>       nr_anon_transparent_hugepages 0
>       nr_vmscan_write 0
>       nr_vmscan_immediate_reclaim 0
>       nr_dirtied   0
>       nr_written   0
>       nr_kernel_misc_reclaimable 0
>       nr_foll_pin_acquired 0
>       nr_foll_pin_released 0
>       nr_kernel_stack 384
>   pages free     1162
>         min      97
>         low      121
>         high     145
>         spanned  8192
>         present  8192
>         managed  3104
>         protection: (0, 0)
>       nr_free_pages 1162
>       nr_zone_inactive_anon 631
>       nr_zone_active_anon 625
>       nr_zone_inactive_file 0
>       nr_zone_active_file 0
>       nr_zone_unevictable 0
>       nr_zone_write_pending 0
>       nr_mlock     0
>       nr_page_table_pages 19
>       nr_bounce    0
>       nr_free_cma  0
>   pagesets
>     cpu: 0
>               count: 0
>               high:  0
>               batch: 1
>   vm stats threshold: 2
>   node_unreclaimable:  0
>   start_pfn:           262144
> Node 0, zone  Movable
>   pages free     0
>         min      0
>         low      0
>         high     0
>         spanned  0
>         present  0
>         managed  0
>         protection: (0, 0)
>
>