linux-kernel - Re: [git pull] cpus4096 tree, part 3

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Message-ID: <20090103213856.GA24138@elte.hu>
Date:	Sat, 3 Jan 2009 22:38:56 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Mike Travis <travis@....com>, linux-kernel@...r.kernel.org,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Arjan van de Ven <arjan@...radead.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [git pull] cpus4096 tree, part 3


* Ingo Molnar <mingo@...e.hu> wrote:

> The test is underway with:
> 
>  CONFIG_64BIT=y
>  CONFIG_NR_CPUS=4096
>  CONFIG_MAXSMP=y

the worst-case stack footprint i was able to trigger on an allyesconfig 
bootup (instrumented via CONFIG_STACK_TRACER=y and the 'stacktrace' boot 
option) was 5.6K:

 # ls -l /debug/tracing/*stack*
 -rw-r--r-- 1 root root 0 2009-01-03 22:42 /debug/tracing/stack_max_size
 -r--r--r-- 1 root root 0 2009-01-03 22:42 /debug/tracing/stack_trace

 # cat /debug/tracing/*stack*
 5624
        Depth   Size      Location    (38 entries)
        -----   ----      --------
  0)     5496     232   lookup_address+0x51/0x20e
  1)     5264     496   __change_page_attr_set_clr+0xa7/0xa15
  2)     4768     128   kernel_map_pages+0x121/0x140
  3)     4640     224   get_page_from_freelist+0x4bb/0x6ec
  4)     4416     160   __alloc_pages_internal+0x150/0x4af
  5)     4256      48   alloc_pages_current+0xbe/0xc7
  6)     4208      16   alloc_slab_page+0x1e/0x6e
  7)     4192      64   new_slab+0x51/0x1e2
  8)     4128      96   __slab_alloc+0x260/0x3fa
  9)     4032      80   kmem_cache_alloc+0xa8/0x120
 10)     3952      48   radix_tree_preload+0x38/0x86
 11)     3904      64   add_to_page_cache_locked+0x51/0xed
 12)     3840      32   add_to_page_cache_lru+0x31/0x6b
 13)     3808      64   find_or_create_page+0x56/0x7d
 14)     3744      80   __getblk+0x136/0x262
 15)     3664      32   __bread+0x13/0x82
 16)     3632      64   ext3_get_branch+0x7b/0xef
 17)     3568     368   ext3_get_blocks_handle+0xa2/0x907
 18)     3200      96   ext3_get_block+0xc3/0x101
 19)     3104     224   do_mpage_readpage+0x1ad/0x4d0
 20)     2880     240   mpage_readpages+0xb6/0xf9
 21)     2640      16   ext3_readpages+0x1f/0x21
 22)     2624     144   __do_page_cache_readahead+0x147/0x1bd
 23)     2480      48   do_page_cache_readahead+0x5b/0x68
 24)     2432     112   filemap_fault+0x176/0x34b
 25)     2320     160   __do_fault+0x58/0x410
 26)     2160     176   handle_mm_fault+0x4b2/0xa3e
 27)     1984     800   do_page_fault+0x86d/0xcec
 28)     1184     208   page_fault+0x25/0x30
 29)      976      16   clear_user+0x30/0x38
 30)      960     288   load_elf_binary+0x61c/0x18f0
 31)      672      80   search_binary_handler+0xd9/0x279
 32)      592     176   load_script+0x1b3/0x1c8
 33)      416      80   search_binary_handler+0xd9/0x279
 34)      336      96   do_execve+0x1df/0x296
 35)      240      64   sys_execve+0x43/0x5e
 36)      176     176   stub_execve+0x6a/0xc0

None of the cpumask_t callsites showed up - but i agree that they should 
be fixed, 512 bytes of cpumask_t on the stack is not good no matter how 
one looks at it, it will only make an already strained kernel stack 
footprint situation worse.

This one looks a bit high:

  1)     5264     496   __change_page_attr_set_clr+0xa7/0xa15

(Venki, Suresh and Arjan Cc:-ed)

This one isnt too nice either:

 27)     1984     800   do_page_fault+0x86d/0xcec

not sure why it happens - will investigate tomorrow, it's getting late 
here.

	Ingo
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