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Index: sys/vm/vm_fault.c
===================================================================
--- sys/vm/vm_fault.c
+++ sys/vm/vm_fault.c
@@ -123,6 +123,7 @@
vm_map_t map;
vm_map_entry_t entry;
int lookup_still_valid;
+ int ra_done;
struct vnode *vp;
};
@@ -292,13 +293,15 @@
struct faultstate fs;
struct vnode *vp;
vm_page_t m;
- int ahead, behind, cluster_offset, error, locked;
+ int ahead, behind, cluster_offset, error, locked, rv;
+ u_char behavior;
hardfault = 0;
growstack = TRUE;
PCPU_INC(cnt.v_vm_faults);
fs.vp = NULL;
faultcount = 0;
+ fs.ra_done = FALSE;
RetryFault:;
@@ -557,9 +560,18 @@
* at the same time.
*/
if (fs.object->type != OBJT_DEFAULT) {
- int rv;
- u_char behavior = vm_map_entry_behavior(fs.entry);
-
+ if (!fs.lookup_still_valid) {
+ locked = vm_map_trylock_read(fs.map);
+ if (locked)
+ fs.lookup_still_valid = TRUE;
+ if (!locked || fs.map->timestamp !=
+ map_generation) {
+ release_page(&fs);
+ unlock_and_deallocate(&fs);
+ goto RetryFault;
+ }
+ }
+ behavior = vm_map_entry_behavior(fs.entry);
era = fs.entry->read_ahead;
if (behavior == MAP_ENTRY_BEHAV_RANDOM ||
P_KILLED(curproc)) {
@@ -570,7 +582,8 @@
behind = 0;
nera = VM_FAULT_READ_AHEAD_MAX;
ahead = nera;
- if (fs.pindex == fs.entry->next_read)
+ if (fs.pindex == fs.entry->next_read &&
+ !fs.ra_done)
vm_fault_dontneed(&fs, vaddr, ahead);
} else if (fs.pindex == fs.entry->next_read) {
/*
@@ -581,14 +594,17 @@
* x (read ahead min + 1) + read ahead min"
*/
behind = 0;
- nera = VM_FAULT_READ_AHEAD_MIN;
- if (era > 0) {
- nera += era + 1;
- if (nera > VM_FAULT_READ_AHEAD_MAX)
- nera = VM_FAULT_READ_AHEAD_MAX;
+ if (!fs.ra_done) {
+ if (era > 0) {
+ nera += era + 1;
+ if (nera > VM_FAULT_READ_AHEAD_MAX)
+ nera = VM_FAULT_READ_AHEAD_MAX;
+ } else
+ nera = VM_FAULT_READ_AHEAD_MIN;
}
ahead = nera;
- if (era == VM_FAULT_READ_AHEAD_MAX)
+ if (era == VM_FAULT_READ_AHEAD_MAX &&
+ !fs.ra_done)
vm_fault_dontneed(&fs, vaddr, ahead);
} else {
/*
@@ -610,7 +626,18 @@
}
ahead = ulmin(ahead, atop(fs.entry->end - vaddr) - 1);
if (era != nera)
+ /*
+ * Only read-lock on map is held
+ * there. It is fine for other thread
+ * faulting on the same entry to race
+ * with us for this update, causing
+ * some inaccuracy in the read-ahead
+ * heuristic. We do not separate two
+ * different streams of sequential
+ * faults on one entry anyway.
+ */
fs.entry->read_ahead = nera;
+ fs.ra_done = TRUE;
/*
* Call the pager to retrieve the data, if any, after
@@ -931,8 +958,10 @@
* 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.
+ * The next_read assignment modifies the map without holding a
+ * write lock on it, which is acceptable. See the motivation
+ * in the comment above, before updating the entry->read_ahead
+ * field in the same manner.
*/
if (hardfault)
fs.entry->next_read = fs.pindex + ahead + 1;

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