On Thursday 15 February 2007 18:09, Jeff Dike wrote:
> On Thu, Feb 15, 2007 at 11:00:01AM -0500, Jason Lunz wrote:
> > Permit lvm to create logical volumes without crashing UML.
>
> Thanks, this is in my tree.
Hmm, this seems not a _correct_ fix - at least it will be buggy with high
memory (which we could drop anyway - actually we _should_ drop it probably).
And at a closer review other potential bugs (or at least misconceptions)
surface.
The difference between low_pfn and pfn should be just high memory accounting -
however also uml_reserved enters the picture, and that is bad.
>From a closer look, it seems that uml_reserved is ignored for max_low_pfn and
considered for max_pfn - with your code, you are going to ignore it
everywhere, while probably you should consider it everywhere (i.e. use
totalram_pages everywhere) - if it is correct to consider it (and I believe
the code was written to do all that for an important reason).
The following could be a suggestion, if max_low_pfn is not used between the
old and the new moment of assignment (and it seems it is not). This is just
an idea however:
mem_init:
- max_low_pfn = ...
/* this will put all low memory onto the freelists */
totalram_pages = free_all_bootmem();
+ max_low_pfn = totalram_pages;
#ifdef CONFIG_HIGHMEM
totalhigh_pages = highmem >> PAGE_SHIFT;
totalram_pages += totalhigh_pages;
#endif
num_physpages = totalram_pages;
max_pfn = totalram_pages;
Please note that I did not spend a lot of time on this, so everything could be
wrong. However, testing cannot help with uml_reserved handling, and this is a
dark corner. So things should be better understood before merging the patch.
The code is too convoluted for a brief look - drawing a picture which explains
all those variables would help. Both for UML and for every arch...
BTW: init_bootmem is not called by us and we probably should - min_low_pfn is
not initialized.
--
Inform me of my mistakes, so I can add them to my list!
Paolo Giarrusso, aka Blaisorblade
http://www.user-mode-linux.org/~blaisorblade
Chiacchiera con i tuoi amici in tempo reale!
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