svn commit: r364729 - stable/12/sys/compat/linux
Mark Johnston
markj at FreeBSD.org
Mon Aug 24 20:02:37 UTC 2020
Author: markj
Date: Mon Aug 24 20:02:36 2020
New Revision: 364729
URL: https://svnweb.freebsd.org/changeset/base/364729
Log:
MFC r362631, r364317:
Implement an approximation of Linux MADV_DONTNEED semantics.
PR: 230160
Modified:
stable/12/sys/compat/linux/linux_mmap.c
Directory Properties:
stable/12/ (props changed)
Modified: stable/12/sys/compat/linux/linux_mmap.c
==============================================================================
--- stable/12/sys/compat/linux/linux_mmap.c Mon Aug 24 20:02:13 2020 (r364728)
+++ stable/12/sys/compat/linux/linux_mmap.c Mon Aug 24 20:02:36 2020 (r364729)
@@ -38,9 +38,11 @@ __FBSDID("$FreeBSD$");
#include <sys/file.h>
#include <sys/imgact.h>
#include <sys/ktr.h>
+#include <sys/lock.h>
#include <sys/mman.h>
#include <sys/proc.h>
#include <sys/resourcevar.h>
+#include <sys/rwlock.h>
#include <sys/syscallsubr.h>
#include <sys/sysent.h>
#include <sys/sysproto.h>
@@ -48,6 +50,7 @@ __FBSDID("$FreeBSD$");
#include <vm/pmap.h>
#include <vm/vm_extern.h>
#include <vm/vm_map.h>
+#include <vm/vm_object.h>
#include <compat/linux/linux_emul.h>
#include <compat/linux/linux_mmap.h>
@@ -233,6 +236,105 @@ linux_mprotect_common(struct thread *td, uintptr_t add
return (kern_mprotect(td, addr, len, prot));
}
+/*
+ * Implement Linux madvise(MADV_DONTNEED), which has unusual semantics: for
+ * anonymous memory, pages in the range are immediately discarded.
+ */
+static int
+linux_madvise_dontneed(struct thread *td, vm_offset_t start, vm_offset_t end)
+{
+ vm_map_t map;
+ vm_map_entry_t entry;
+ vm_object_t backing_object, object;
+ vm_offset_t estart, eend;
+ vm_pindex_t pstart, pend;
+ int error;
+
+ map = &td->td_proc->p_vmspace->vm_map;
+
+ if (!vm_map_range_valid(map, start, end))
+ return (EINVAL);
+ start = trunc_page(start);
+ end = round_page(end);
+
+ error = 0;
+ vm_map_lock_read(map);
+ if (!vm_map_lookup_entry(map, start, &entry))
+ entry = entry->next;
+ for (; entry->start < end; entry = entry->next) {
+ if ((entry->eflags & MAP_ENTRY_IS_SUB_MAP) != 0)
+ continue;
+
+ if (entry->wired_count != 0) {
+ error = EINVAL;
+ break;
+ }
+
+ object = entry->object.vm_object;
+ if (object == NULL)
+ continue;
+ if ((object->flags & (OBJ_UNMANAGED | OBJ_FICTITIOUS)) != 0)
+ continue;
+
+ pstart = OFF_TO_IDX(entry->offset);
+ if (start > entry->start) {
+ pstart += atop(start - entry->start);
+ estart = start;
+ } else {
+ estart = entry->start;
+ }
+ pend = OFF_TO_IDX(entry->offset) +
+ atop(entry->end - entry->start);
+ if (entry->end > end) {
+ pend -= atop(entry->end - end);
+ eend = end;
+ } else {
+ eend = entry->end;
+ }
+
+ if ((object->type == OBJT_DEFAULT ||
+ object->type == OBJT_SWAP) && object->handle == NULL &&
+ (object->flags & (OBJ_ONEMAPPING | OBJ_NOSPLIT)) ==
+ OBJ_ONEMAPPING) {
+ /*
+ * Singly-mapped anonymous memory is discarded. This
+ * does not match Linux's semantics when the object
+ * belongs to a shadow chain of length > 1, since
+ * subsequent faults may retrieve pages from an
+ * intermediate anonymous object. However, handling
+ * this case correctly introduces a fair bit of
+ * complexity.
+ */
+ VM_OBJECT_WLOCK(object);
+ if ((object->flags & OBJ_ONEMAPPING) != 0) {
+ vm_object_collapse(object);
+ vm_object_page_remove(object, pstart, pend, 0);
+ backing_object = object->backing_object;
+ if (backing_object != NULL &&
+ (backing_object->type == OBJT_DEFAULT ||
+ backing_object->type == OBJT_SWAP) &&
+ backing_object->handle == NULL &&
+ (backing_object->flags & OBJ_NOSPLIT) == 0)
+ linux_msg(td,
+ "possibly incorrect MADV_DONTNEED");
+ VM_OBJECT_WUNLOCK(object);
+ continue;
+ }
+ VM_OBJECT_WUNLOCK(object);
+ }
+
+ /*
+ * Handle shared mappings. Remove them outright instead of
+ * calling pmap_advise(), for consistency with Linux.
+ */
+ pmap_remove(map->pmap, estart, eend);
+ vm_object_madvise(object, pstart, pend, MADV_DONTNEED);
+ }
+ vm_map_unlock_read(map);
+
+ return (error);
+}
+
int
linux_madvise_common(struct thread *td, uintptr_t addr, size_t len, int behav)
{
@@ -247,7 +349,7 @@ linux_madvise_common(struct thread *td, uintptr_t addr
case LINUX_MADV_WILLNEED:
return (kern_madvise(td, addr, len, MADV_WILLNEED));
case LINUX_MADV_DONTNEED:
- return (kern_madvise(td, addr, len, MADV_DONTNEED));
+ return (linux_madvise_dontneed(td, addr, addr + len));
case LINUX_MADV_FREE:
return (kern_madvise(td, addr, len, MADV_FREE));
case LINUX_MADV_REMOVE:
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