Re: [PATCH v3 1/2] Generic handling of multi-page exclusions

[HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>]

From: Atsushi Kumagai <kumagai-atsushi@mxc.nes.nec.co.jp>
Subject: RE: [PATCH v3 1/2] Generic handling of multi-page exclusions
Date: Wed, 14 May 2014 07:54:17 +0000

> Hello Petr,
> 
>>When multiple pages are excluded from the dump, store the extents in
>>struct cycle and check if anything is still pending on the next invocation
>>of __exclude_unnecessary_pages. This assumes that:
>>
>>  1. after __exclude_unnecessary_pages is called for a struct mem_map_data
>>     that extends beyond the current cycle, it is not called again during
>>     that cycle,
>>  2. in the next cycle, __exclude_unnecessary_pages is not called before
>>     this final struct mem_map_data.
>>
>>Both assumptions are met if struct mem_map_data segments:
>>
>>  1. do not overlap,
>>  2. are sorted by physical address in ascending order.
> 
> In ELF case, write_elf_pages_cyclic() processes PT_LOAD entries from
> PT_LOAD(0), this can break both assumptions unluckily.
> Actually this patch doesn't work on my machine:
> 
> LOAD (0)
>   phys_start : 1000000
>   phys_end   : 182f000
>   virt_start : ffffffff81000000
>   virt_end   : ffffffff8182f000
> LOAD (1)
>   phys_start : 1000
>   phys_end   : 9b400
>   virt_start : ffff810000001000
>   virt_end   : ffff81000009b400
> LOAD (2)
>   phys_start : 100000
>   phys_end   : 27000000
>   virt_start : ffff810000100000
>   virt_end   : ffff810027000000
> LOAD (3)
>   phys_start : 37000000
>   phys_end   : cff70000
>   virt_start : ffff810037000000
>   virt_end   : ffff8100cff70000
> LOAD (4)
>   phys_start : 100000000
>   phys_end   : 170000000
>   virt_start : ffff810100000000
>   virt_end   : ffff810170000000
> 
> 
> PT_LOAD(2) includes PT_LOAD(0) and there physical addresses aren't sorted.
> 
> If there is the only "sort issue", it may easy to fix it with a new iterator
> like "for_each_pt_load()", it iterates PT_LOAD entries in ascending order
> by physical address.
> However, I don't have a good idea to solve the overlap issue now...
> 

Is it enough to merge them? Prepare a modified version of PTLOAD list
and refer to it in actual processing. I think this also leads to
cleaning up readpage_elf() that addresses some overapping memory map
issue on ia64.

--
Thanks.
HATAYAMA, Daisuke


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