[PATCH resend v3 1/2] ntdll: Try mapping free memory region outside of reserved regions.

Rémi Bernon rbernon at codeweavers.com
Tue Dec 24 08:32:57 CST 2019

On 12/24/19 3:23 PM, Paul Gofman wrote:
> On 12/24/19 16:17, Rémi Bernon wrote:
>> On 12/24/19 1:27 PM, Alexandre Julliard wrote:
>> The original patches this whole zero bits thing is based upon were
>> trying semi-random addresses to try to find free system areas, with a
>> timeout [1], but I'm not completely convinced that it's better
>> especially with the top_down flag to implement.
>> It could also read /proc/self/maps, making it not portable, I guess.
>> Or maybe there's a way to enumerate mapped memory, including non-Wine,
>> that I'm missing?
> Just to mention, there is also an mincore() system call which I suppose
> should be portable which can provide a preliminary guess if the range of
> pages is free. It should be much less expensive than an attempt to map a
> memory at least because the attempt always succeeds allocating the
> memory outside of the region which is then freed in case memory is busy.
> This is still not transactional of course (native code in separate
> threads can get the memory right after checking it availability either way).

Alright, I didn't know that, thanks.

>> Or you just mean the search within an expected free area could do a
>> bisection instead of iterating linearly?
> There are some applications which depend on (virtual) memory allocations
> not returning high addresses while the lower memory is available.
> Windows allocates virtual memory bottom up unless top down is explicitly
> requested. I made a patch [1] some time ago which does that the same way
> zero_bits allocation works (that depends on this fix or equivalent).
> Unless such sort of change is not desirable for some reason it would be
> great if the modified fix for zero_bits support would keep the ability
> to follow bottom up / top down allocation order.

Sure, and by bisection I rather meant that -assuming the requested size 
is greater than the alignment- you can probably start iterating with a 
bigger step to have a coarse estimate before trying to find a more 
precise location.
Rémi Bernon <rbernon at codeweavers.com>

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