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Cygwin: shmat: use mmap allocator strategy on 64 bit

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This avoids collisions of shmat maps with Windows own datastructures
when allocating top-down.

This patch moves the mmap_allocator class definition into its
own files and just uses it from mmap and shmat.
This commit is contained in:
Corinna Vinschen 2019-08-08 10:53:58 +02:00
parent 5fa9a0e708
commit 1f34405fea
5 changed files with 109 additions and 89 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
winsup/cygwin/Makefile.in
View File

@ -341,6 +341,7 @@ DLL_OFILES:= \
miscfuncs.o \
mktemp.o \
mmap.o \
mmap_alloc.o \
msg.o \
msgcat.o \
mount.o \

89
winsup/cygwin/mmap.cc
View File

@ -20,6 +20,7 @@ details. */
#include "cygheap.h"
#include "ntdll.h"
#include <sys/queue.h>
#include "mmap_alloc.h"
/* __PROT_ATTACH indicates an anonymous mapping which is supposed to be
attached to a file mapping for pages beyond the file's EOF. The idea
@ -798,94 +799,6 @@ mmap_worker (mmap_list *map_list, fhandler_base *fh, caddr_t base, size_t len,
return base;
}
#ifdef __x86_64__
/* The memory region used for memory maps */
#define MMAP_STORAGE_LOW 0x001000000000L /* Leave 32 Gigs for heap. */
/* Up to Win 8 only supporting 44 bit address space, starting with Win 8.1
48 bit address space. */
#define MMAP_STORAGE_HIGH wincap.mmap_storage_high ()
/* 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.
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. */
class mmap_allocator
{
caddr_t mmap_current_low;
public:
mmap_allocator () : mmap_current_low ((caddr_t) MMAP_STORAGE_HIGH) {}
PVOID alloc (PVOID in_addr, SIZE_T in_size, bool fixed)
{
MEMORY_BASIC_INFORMATION mbi;
SIZE_T size = roundup2 (in_size, wincap.allocation_granularity ());
/* First check for the given address. */
if (in_addr)
{
/* If it points to a free area, big enough to fulfill the request,
return the address. */
if (VirtualQuery (in_addr, &mbi, sizeof mbi)
&& mbi.State == MEM_FREE
&& mbi.RegionSize >= size)
return in_addr;
/* Otherwise, if MAP_FIXED was given, give up. */
if (fixed)
return NULL;
/* Otherwise, fall through to the usual free space search mechanism. */
}
/* Start with the last allocation start address - requested size. */
caddr_t addr = mmap_current_low - size;
bool merry_go_round = false;
do
{
/* Did we hit the lower ceiling? If so, restart from the upper
ceiling, but note that we did it. */
if (addr < (caddr_t) MMAP_STORAGE_LOW)
{
addr = (caddr_t) MMAP_STORAGE_HIGH - size;
merry_go_round = true;
}
/* Shouldn't fail, but better test. */
if (!VirtualQuery ((PVOID) addr, &mbi, sizeof mbi))
return NULL;
/* If the region is free... */
if (mbi.State == MEM_FREE)
{
/* ...and the region is big enough to fulfill the request... */
if (mbi.RegionSize >= size)
{
/* ...note the address as next start address for our simple
merry-go-round and return the address. */
mmap_current_low = addr;
return (PVOID) addr;
}
/* Otherwise, subtract what's missing in size and try again. */
addr -= size - mbi.RegionSize;
}
/* If the region isn't free, skip to address below AllocationBase
and try again. */
else
addr = (caddr_t) mbi.AllocationBase - size;
}
/* Repeat until we had a full ride on the merry_go_round. */
while (!merry_go_round || addr >= mmap_current_low);
return NULL;
}
};
static mmap_allocator mmap_alloc; /* Inherited by forked child. */
#endif
extern "C" void *
mmap64 (void *addr, size_t len, int prot, int flags, int fd, off_t off)
{

79
winsup/cygwin/mmap_alloc.cc Normal file
View File

@ -0,0 +1,79 @@
#ifdef __x86_64__
#include "winsup.h"
#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.
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)
{
MEMORY_BASIC_INFORMATION mbi;
SIZE_T size = roundup2 (in_size, wincap.allocation_granularity ());
/* First check for the given address. */
if (in_addr)
{
/* If it points to a free area, big enough to fulfill the request,
return the address. */
if (VirtualQuery (in_addr, &mbi, sizeof mbi)
&& mbi.State == MEM_FREE
&& mbi.RegionSize >= size)
return in_addr;
/* Otherwise, if MAP_FIXED was given, give up. */
if (fixed)
return NULL;
/* Otherwise, fall through to the usual free space search mechanism. */
}
/* Start with the last allocation start address - requested size. */
caddr_t addr = mmap_current_low - size;
bool merry_go_round = false;
do
{
/* Did we hit the lower ceiling? If so, restart from the upper
ceiling, but note that we did it. */
if (addr < (caddr_t) MMAP_STORAGE_LOW)
{
addr = (caddr_t) MMAP_STORAGE_HIGH - size;
merry_go_round = true;
}
/* Shouldn't fail, but better test. */
if (!VirtualQuery ((PVOID) addr, &mbi, sizeof mbi))
return NULL;
/* If the region is free... */
if (mbi.State == MEM_FREE)
{
/* ...and the region is big enough to fulfill the request... */
if (mbi.RegionSize >= size)
{
/* ...note the address as next start address for our simple
merry-go-round and return the address. */
mmap_current_low = addr;
return (PVOID) addr;
}
/* Otherwise, subtract what's missing in size and try again. */
addr -= size - mbi.RegionSize;
}
/* If the region isn't free, skip to address below AllocationBase
and try again. */
else
addr = (caddr_t) mbi.AllocationBase - size;
}
/* Repeat until we had a full ride on the merry_go_round. */
while (!merry_go_round || addr >= mmap_current_low);
return NULL;
}
mmap_allocator mmap_alloc; /* Inherited by forked child. */
#endif

21
winsup/cygwin/mmap_alloc.h Normal file
View File

@ -0,0 +1,21 @@
#ifdef __x86_64__
/* The memory region used for memory maps */
#define MMAP_STORAGE_LOW 0x001000000000L /* Leave 32 Gigs for heap. */
/* Up to Win 8 only supporting 44 bit address space, starting with Win 8.1
48 bit address space. */
#define MMAP_STORAGE_HIGH wincap.mmap_storage_high ()
class mmap_allocator
{
caddr_t mmap_current_low;
public:
mmap_allocator () : mmap_current_low ((caddr_t) MMAP_STORAGE_HIGH) {}
PVOID alloc (PVOID in_addr, SIZE_T in_size, bool fixed);
};
extern mmap_allocator mmap_alloc;
#endif

8
winsup/cygwin/shm.cc
View File

@ -17,6 +17,7 @@ details. */
#include "cygtls.h"
#include "sync.h"
#include "ntdll.h"
#include "mmap_alloc.h"
/* __getpagesize is only available from libcygwin.a */
#undef SHMLBA
@ -220,8 +221,13 @@ shmat (int shmid, const void *shmaddr, int shmflg)
return (void *) -1;
}
NTSTATUS status;
vm_object_t ptr = NULL;
SIZE_T viewsize = ssh_entry->size;
#ifdef __x86_64__
vm_object_t ptr = mmap_alloc.alloc (NULL, viewsize, false);
#else
vm_object_t ptr = NULL;
#endif
ULONG access = (shmflg & SHM_RDONLY) ? PAGE_READONLY : PAGE_READWRITE;
status = NtMapViewOfSection (ssh_entry->hdl, NtCurrentProcess (), &ptr, 0,
ssh_entry->size, NULL, &viewsize, ViewShare,