Date: Sun, 16 Jun 2002 22:19:19 -0600 From: "Kenneth D. Merry" <ken@kdm.org> To: current@FreeBSD.org Cc: alc@FreeBSD.org Subject: vm_object_allocate() question Message-ID: <20020616221919.A78576@panzer.kdm.org>
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As part of my zero copy patches, I have to allocate a vm object.
To keep the object pointer from potentially getting spammed, I have it
protected by a mutex.
vm_object_allocate() calls uma_zalloc() with the M_WAITOK flag, therefore
WITNESS complains that we could sleep with a mutex held.
There are two obvious solutions to the problem, and I'd like some opinions
on which is the better approach:
1. Allocate my vm object and assign it to a temporary variable in
jumbo_vm_init() outside the mutex protection. Only assign it to the
right pointer if we haven't already been initialized.
This would work, but seems like it would be a bit of an unnecessary
step.
2. Change vm_object_allocate() somehow so that uma_zalloc() isn't called
with M_WAITOK.
I've attached patches for the second option. I created a new function,
vm_object_allocate_wait(), that allows the user to specify whether or not
to wait on the uma_zalloc() call.
vm_object_allocate() is a wrapper for the new vm_object_allocate_wait()
call that preserves the current behavior.
Patches are attached, comments would be appreciated!
Thanks,
Ken
--
Kenneth Merry
ken@kdm.org
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==== //depot/FreeBSD-zero/src/sys/kern/uipc_jumbo.c#3 - /usr/home/ken/perforce/FreeBSD-zero/src/sys/kern/uipc_jumbo.c ====
*** /tmp/tmp.72862.0 Sun Jun 16 22:11:05 2002
--- /usr/home/ken/perforce/FreeBSD-zero/src/sys/kern/uipc_jumbo.c Sun Jun 16 21:39:21 2002
***************
*** 101,107 ****
}
/* allocate our object */
! jumbo_vm_object = vm_object_allocate(OBJT_DEFAULT, JUMBO_MAX_PAGES);
SLIST_INIT(&jumbo_kmap_free);
SLIST_INIT(&jumbo_kmap_inuse);
--- 101,113 ----
}
/* allocate our object */
! jumbo_vm_object = vm_object_allocate_wait(OBJT_DEFAULT, JUMBO_MAX_PAGES,
! M_NOWAIT);
!
! if (jumbo_vm_object == NULL) {
! mtx_unlock(&jumbo_mutex);
! return (0);
! }
SLIST_INIT(&jumbo_kmap_free);
SLIST_INIT(&jumbo_kmap_inuse);
==== //depot/FreeBSD-zero/src/sys/vm/vm_object.c#13 - /usr/home/ken/perforce/FreeBSD-zero/src/sys/vm/vm_object.c ====
*** /tmp/tmp.72862.1 Sun Jun 16 22:11:05 2002
--- /usr/home/ken/perforce/FreeBSD-zero/src/sys/vm/vm_object.c Wed Jun 5 21:28:48 2002
***************
*** 336,354 ****
}
/*
! * vm_object_allocate:
*
! * Returns a new object with the given size.
*/
vm_object_t
! vm_object_allocate(objtype_t type, vm_size_t size)
{
vm_object_t result;
! result = (vm_object_t) uma_zalloc(obj_zone, M_WAITOK);
! _vm_object_allocate(type, size, result);
return (result);
}
--- 336,369 ----
}
/*
! * vm_object_allocate_wait
*
! * Return a new object with the given size, and give the user the
! * option of waiting for it to complete or failing if the needed
! * memory isn't available.
*/
vm_object_t
! vm_object_allocate_wait(objtype_t type, vm_size_t size, int flags)
{
vm_object_t result;
! result = (vm_object_t) uma_zalloc(obj_zone, flags);
!
! if (result != NULL)
! _vm_object_allocate(type, size, result);
return (result);
+ }
+
+ /*
+ * vm_object_allocate:
+ *
+ * Returns a new object with the given size.
+ */
+ vm_object_t
+ vm_object_allocate(objtype_t type, vm_size_t size)
+ {
+ return(vm_object_allocate_wait(type, size, M_WAITOK));
}
==== //depot/FreeBSD-zero/src/sys/vm/vm_object.h#7 - /usr/home/ken/perforce/FreeBSD-zero/src/sys/vm/vm_object.h ====
*** /tmp/tmp.72862.2 Sun Jun 16 22:11:05 2002
--- /usr/home/ken/perforce/FreeBSD-zero/src/sys/vm/vm_object.h Wed Jun 5 21:28:57 2002
***************
*** 183,188 ****
--- 183,189 ----
void vm_object_pip_wait(vm_object_t object, char *waitid);
vm_object_t vm_object_allocate (objtype_t, vm_size_t);
+ vm_object_t vm_object_allocate_wait (objtype_t, vm_size_t, int);
void _vm_object_allocate (objtype_t, vm_size_t, vm_object_t);
boolean_t vm_object_coalesce (vm_object_t, vm_pindex_t, vm_size_t, vm_size_t);
void vm_object_collapse (vm_object_t);
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