Author: alc
Date: Thu Jul 7 20:58:16 2016
New Revision: 302399
URL: https://svnweb.freebsd.org/changeset/base/302399
Log:
Change the type of the map entry's next_read field from a vm_pindex_t to a
vm_offset_t. (This field is used to detect sequential access to the virtual
address range represented by the map entry.) There are three reasons to
make this change. First, a vm_offset_t is smaller on 32-bit architectures.
Consequently, a struct vm_map_entry is now smaller on 32-bit architectures.
Second, a vm_offset_t can be written atomically, whereas it may not be
possible to write a vm_pindex_t atomically on a 32-bit architecture. Third,
using a vm_pindex_t makes the next_read field dependent on which object in
the shadow chain is being read from.
Replace an "XXX" comment.
Reviewed by: kib
Approved by: re (gjb)
Sponsored by: EMC / Isilon Storage Division
Modified:
head/sys/vm/vm_fault.c
head/sys/vm/vm_map.c
head/sys/vm/vm_map.h
Modified: head/sys/vm/vm_fault.c
==============================================================================
--- head/sys/vm/vm_fault.c Thu Jul 7 20:50:59 2016 (r302398)
+++ head/sys/vm/vm_fault.c Thu Jul 7 20:58:16 2016 (r302399)
@@ -570,9 +570,9 @@ readrest:
behind = 0;
nera = VM_FAULT_READ_AHEAD_MAX;
ahead = nera;
- if (fs.pindex == fs.entry->next_read)
+ if (vaddr == fs.entry->next_read)
vm_fault_dontneed(&fs, vaddr, ahead);
- } else if (fs.pindex == fs.entry->next_read) {
+ } else if (vaddr == fs.entry->next_read) {
/*
* This is a sequential fault. Arithmetically
* increase the requested number of pages in
@@ -927,15 +927,15 @@ vnode_locked:
prot &= retry_prot;
}
}
+
/*
- * If the page was filled by a pager, update the map entry's
- * last read offset.
- *
- * XXX The following assignment modifies the map
- * without holding a write lock on it.
+ * If the page was filled by a pager, save the virtual address that
+ * should be faulted on next under a sequential access pattern to the
+ * map entry. A read lock on the map suffices to update this address
+ * safely.
*/
if (hardfault)
- fs.entry->next_read = fs.pindex + ahead + 1;
+ fs.entry->next_read = vaddr + ptoa(ahead) + PAGE_SIZE;
vm_fault_dirty(fs.entry, fs.m, prot, fault_type, fault_flags, TRUE);
vm_page_assert_xbusied(fs.m);
Modified: head/sys/vm/vm_map.c
==============================================================================
--- head/sys/vm/vm_map.c Thu Jul 7 20:50:59 2016 (r302398)
+++ head/sys/vm/vm_map.c Thu Jul 7 20:58:16 2016 (r302399)
@@ -1330,7 +1330,7 @@ charged:
new_entry->wired_count = 0;
new_entry->wiring_thread = NULL;
new_entry->read_ahead = VM_FAULT_READ_AHEAD_INIT;
- new_entry->next_read = OFF_TO_IDX(offset);
+ new_entry->next_read = start;
KASSERT(cred == NULL || !ENTRY_CHARGED(new_entry),
("OVERCOMMIT: vm_map_insert leaks vm_map %p", new_entry));
Modified: head/sys/vm/vm_map.h
==============================================================================
--- head/sys/vm/vm_map.h Thu Jul 7 20:50:59 2016 (r302398)
+++ head/sys/vm/vm_map.h Thu Jul 7 20:58:16 2016 (r302399)
@@ -104,6 +104,7 @@ struct vm_map_entry {
vm_offset_t start; /* start address */
vm_offset_t end; /* end address */
vm_offset_t avail_ssize; /* amt can grow if this is a stack */
+ vm_offset_t next_read; /* vaddr of the next sequential read */
vm_size_t adj_free; /* amount of adjacent free space */
vm_size_t max_free; /* max free space in subtree */
union vm_map_object object; /* object I point to */
@@ -114,7 +115,6 @@ struct vm_map_entry {
vm_inherit_t inheritance; /* inheritance */
uint8_t read_ahead; /* pages in the read-ahead window */
int wired_count; /* can be paged if = 0 */
- vm_pindex_t next_read; /* index of the next sequential read */
struct ucred *cred; /* tmp storage for creator ref */
struct thread *wiring_thread;
};
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