IGBPI?I1I? 23/06/2017 10:13 I?I 1/4 , I? Michal Hocko I-I3I?I+-I?Iu:

On Thu 22-06-17 12:37:36, Andrew Morton wrote:

What is your dirty limit configuration. Is your highmem dirtyable
(highmem_is_dirtyable)?

quoted

quoted

This issue happens on systems with any 4.x kernel, i386 arch, 16+ GB RAM.
It doesn't happen if we use 3.x kernels (i.e. it's a regression) or any 64bit
kernels (i.e. it only affects i386).

I remember we've had some changes in the way how the dirty memory is
throttled and 32b would be more sensitive to those changes. Anyway, I
would _strongly_ discourage you from using 32b kernels with that much of
memory. You are going to hit walls constantly and many of those issues
will be inherent. Some of them less so but rather non-trivial to fix
without regressing somewhere else. You can tune your system somehow but
this will be fragile no mater what.

Sorry to say that but 32b systems with tons of memory are far from
priority of most mm people. Just use 64b kernel. There are more pressing
problems to deal with.

Hi, I'm attaching below all my settings from /proc/sys/vm.

I think that the regression also affects 4 GB and 8 GB RAM i386 systems, 
but not in an exponential manner; i.e. copies there are appear only 2-3 
times slower than they used to be in 3.x kernels.

Now I don't know the kernel internals, but if disk copies show up to be 
2-3 times slower, and the regression is in memory management, wouldn't 
that mean that the memory management is *hundreds* of times slower, to 
show up in disk writing benchmarks?

I.e. I'm afraid that this regression doesn't affect 16+ GB RAM systems 
only; it just happens that it's clearly visible there.

And it might even affect 64bit systems with even more RAM; but I don't 
have any such system to test with.

Kind regards,
Alkis


root@pc:/proc/sys/vm# grep . *
admin_reserve_kbytes:8192
block_dump:0
compact_unevictable_allowed:1
dirty_background_bytes:0
dirty_background_ratio:10
dirty_bytes:0
dirty_expire_centisecs:1500
dirty_ratio:20
dirtytime_expire_seconds:43200
dirty_writeback_centisecs:1500
drop_caches:3
extfrag_threshold:500
highmem_is_dirtyable:0
hugepages_treat_as_movable:0
hugetlb_shm_group:0
laptop_mode:0
legacy_va_layout:0
lowmem_reserve_ratio:256	32	32
max_map_count:65530
min_free_kbytes:34420
mmap_min_addr:65536
mmap_rnd_bits:8
nr_hugepages:0
nr_overcommit_hugepages:0
nr_pdflush_threads:0
oom_dump_tasks:1
oom_kill_allocating_task:0
overcommit_kbytes:0
overcommit_memory:0
overcommit_ratio:50
page-cluster:3
panic_on_oom:0
percpu_pagelist_fraction:0
stat_interval:1
swappiness:60
user_reserve_kbytes:131072
vdso_enabled:1
vfs_cache_pressure:100
watermark_scale_factor:10

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