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Cygwin: mmap_alloc: fix comment to document using the extended memory API 

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
This commit is contained in:
Corinna Vinschen 2020-04-07 14:17:04 +02:00 committed by Ken Brown
parent 725b690bba
commit b6df67537b
1 changed files with 13 additions and 10 deletions
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23
winsup/cygwin/mmap_alloc.cc
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@ -4,17 +4,20 @@
#include "mmap_alloc.h"
#include <sys/param.h>
/* FIXME? Unfortunately the OS doesn't support a top down allocation with
a ceiling value. The ZeroBits mechanism only works for
NtMapViewOfSection and it only evaluates the high bit of ZeroBits
on 64 bit, so it's pretty much useless for our purposes.
/* Starting with Windows 10 1803 we use VirtualAlloc2 and MapViewOfFile3
(or rather NtMapViewOfSectionEx), rather than the below class.
Up to Windows 10 1709, the OS doesn't support a top down allocation with
a ceiling value. The ZeroBits mechanism only works for NtMapViewOfSection
and it only evaluates the high bit of ZeroBits on 64 bit, so it's pretty
much useless for our purposes.
If the below simple mechanism to perform top-down allocations turns out to
be too dumb, we need something else. One idea is to divide the space in
(3835) 4 Gig chunks and just store the available free space per slot. Then
we can go top down from slot to slot and only try slots which are supposed
to have enough space. Bookkeeping would be very simple and fast. */
If the below simple mechanism to perform top-down allocations
turns out to be too dumb, we need something else. One idea is to
dived the space in (3835) 4 Gig chunks and simply store the
available free space per slot. Then we can go top down from slot
to slot and only try slots which are supposed to have enough space.
Bookkeeping would be very simple and fast. */
PVOID
mmap_allocator::alloc (PVOID in_addr, SIZE_T in_size, bool fixed)
{