[newlib-cygwin/main] Cygwin: mmap: use 64K pages for bookkeeping

[Ken Brown]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=74017d229d5e46867c8a3ec01bf653e4392bf14c

commit 74017d229d5e46867c8a3ec01bf653e4392bf14c
Author: Ken Brown <kbrown@cornell.edu>
Date:   Fri Jan 10 14:39:46 2025 -0500

    Cygwin: mmap: use 64K pages for bookkeeping
    
    It was convenient to use pages of size 4K (Windows page size) for
    bookkeeping when we were using filler pages.  But all references to
    filler pages were removed in commit ceda26c9d35b ("Cygwin: mmap:
    remove __PROT_FILLER and the associated methods"), so this is no
    longer necessary.  Switch to using pages of size 64K (Windows
    allocation granularity) for everything.
    
    Signed-off-by: Ken Brown <kbrown@cornell.edu>

Diff:
---
 winsup/cygwin/mm/mmap.cc | 29 ++++++++++++++++-------------
 1 file changed, 16 insertions(+), 13 deletions(-)

diff --git a/winsup/cygwin/mm/mmap.cc b/winsup/cygwin/mm/mmap.cc
index 501d37bb2..9c10d5e2a 100644
--- a/winsup/cygwin/mm/mmap.cc
+++ b/winsup/cygwin/mm/mmap.cc
@@ -28,8 +28,8 @@ details. */
    to mapping length (POSIX semantics). */
 #define __PROT_ATTACH   0x8000000
 
-/* Stick with 4K pages for bookkeeping. */
-#define PAGE_CNT(bytes) howmany((bytes), wincap.page_size())
+/* Use 64K pages throughout. */
+#define PAGE_CNT(bytes) howmany((bytes), wincap.allocation_granularity())
 
 #define PGBITS		(sizeof (DWORD)*8)
 #define MAPSIZE(pages)	howmany ((pages), PGBITS)
@@ -418,7 +418,7 @@ mmap_record::match (caddr_t addr, SIZE_T len, caddr_t &m_addr, SIZE_T &m_len,
 		    bool &contains)
 {
   contains = false;
-  SIZE_T rec_len = PAGE_CNT (get_len ()) * wincap.page_size ();
+  SIZE_T rec_len = PAGE_CNT (get_len ()) * wincap.allocation_granularity ();
   caddr_t low = MAX (addr, get_address ());
   caddr_t high = MIN (addr + len, get_address () + rec_len);
   if (low < high)
@@ -470,8 +470,9 @@ mmap_record::map_pages (SIZE_T len, int new_prot, off_t off)
   len = PAGE_CNT (len);
 
   if (!noreserve ()
-      && !VirtualProtect (get_address () + off * wincap.page_size (),
-			  len * wincap.page_size (),
+      && !VirtualProtect (get_address ()
+			  + off * wincap.allocation_granularity (),
+			  len * wincap.allocation_granularity (),
 			  ::gen_protect (new_prot, get_flags ()),
 			  &old_prot))
     {
@@ -491,7 +492,7 @@ mmap_record::map_pages (caddr_t addr, SIZE_T len, int new_prot)
 		new_prot);
   DWORD old_prot;
   off_t off = addr - get_address ();
-  off /= wincap.page_size ();
+  off /= wincap.allocation_granularity ();
   len = PAGE_CNT (len);
   /* VirtualProtect can only be called on committed pages, so it's not
      clear how to change protection in the noreserve case.  In this
@@ -507,8 +508,9 @@ mmap_record::map_pages (caddr_t addr, SIZE_T len, int new_prot)
 	    return false;
 	  }
     }
-  else if (!VirtualProtect (get_address () + off * wincap.page_size (),
-			    len * wincap.page_size (),
+  else if (!VirtualProtect (get_address ()
+			    + off * wincap.allocation_granularity (),
+			    len * wincap.allocation_granularity (),
 			    ::gen_protect (new_prot, get_flags ()),
 			    &old_prot))
     {
@@ -532,7 +534,7 @@ mmap_record::unmap_pages (caddr_t addr, SIZE_T len)
 			    &old_prot))
     debug_printf ("VirtualProtect in unmap_pages () failed, %E");
 
-  off /= wincap.page_size ();
+  off /= wincap.allocation_granularity ();
   len = PAGE_CNT (len);
   for (; len-- > 0; ++off)
     MAP_CLR (off);
@@ -549,7 +551,7 @@ mmap_record::access (caddr_t address)
 {
   if (address < get_address () || address >= get_address () + get_len ())
     return 0;
-  SIZE_T off = (address - get_address ()) / wincap.page_size ();
+  SIZE_T off = (address - get_address ()) / wincap.allocation_granularity ();
   return MAP_ISSET (off);
 }
 
@@ -642,7 +644,8 @@ mmap_list::try_map (void *addr, size_t len, int new_prot, int flags, off_t off)
 	{
 	  if (!rec->map_pages (len, new_prot, off))
 	    return (caddr_t) MAP_FAILED;
-	  return (caddr_t) rec->get_address () + off * wincap.page_size ();
+	  return (caddr_t) rec->get_address ()
+	    + off * wincap.allocation_granularity ();
 	}
     }
   else if (fixed (flags))
@@ -879,8 +882,8 @@ mmap (void *addr, size_t len, int prot, int flags, int fd, off_t off)
       /* The autoconf mmap test maps a file of size 1 byte.  It then tests
 	 every byte of the entire mapped page of 64K for 0-bytes since that's
 	 what POSIX requires.  The problem is, we can't create that mapping.
-	 The file mapping will be only a single page, 4K, and the remainder
-	 of the 64K slot will result in a SEGV when accessed.
+	 The file mapping will be only a single Windows page, 4K, and the
+	 remainder of the 64K slot will result in a SEGV when accessed.
 
 	 So, what we do here is cheating for the sake of the autoconf test.
 	 The justification is that there's very likely no application actually