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diff --git a/sys/vm/swap_pager.c b/sys/vm/swap_pager.c
--- a/sys/vm/swap_pager.c
+++ b/sys/vm/swap_pager.c
@@ -469,7 +469,8 @@
static void swp_pager_free_empty_swblk(vm_object_t, struct swblk *sb);
static int swapongeom(struct vnode *);
static int swaponvp(struct thread *, struct vnode *, u_long);
-static int swapoff_one(struct swdevt *sp, struct ucred *cred);
+static int swapoff_one(struct swdevt *sp, struct ucred *cred,
+ bool ignore_check);
/*
* Swap bitmap functions
@@ -2523,14 +2524,14 @@
error = EINVAL;
goto done;
}
- error = swapoff_one(sp, td->td_ucred);
+ error = swapoff_one(sp, td->td_ucred, false);
done:
sx_xunlock(&swdev_syscall_lock);
return (error);
}
static int
-swapoff_one(struct swdevt *sp, struct ucred *cred)
+swapoff_one(struct swdevt *sp, struct ucred *cred, bool ignore_check)
{
u_long nblks;
#ifdef MAC
@@ -2552,8 +2553,16 @@
* available virtual memory in the system will fit the amount
* of data we will have to page back in, plus an epsilon so
* the system doesn't become critically low on swap space.
+ * The vm_free_count() part does not account e.g. for clean
+ * pages that can be immediately reclaimed without paging, so
+ * this is a very rough estimation.
+ *
+ * On the other hand, not turning swap off on swapoff_all()
+ * means that we can lose swap data when filesystems go away,
+ * which is arguably worse.
*/
- if (vm_free_count() + swap_pager_avail < nblks + nswap_lowat)
+ if (!ignore_check &&
+ vm_free_count() + swap_pager_avail < nblks + nswap_lowat)
return (ENOMEM);
/*
@@ -2603,7 +2612,7 @@
devname = devtoname(sp->sw_vp->v_rdev);
else
devname = "[file]";
- error = swapoff_one(sp, thread0.td_ucred);
+ error = swapoff_one(sp, thread0.td_ucred, true);
if (error != 0) {
printf("Cannot remove swap device %s (error=%d), "
"skipping.\n", devname, error);

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