panic in uma_startup for many-core amd64 system

[Giovanni Trematerra]

On Tue, Oct 19, 2010 at 8:55 AM, Andriy Gapon <avg at freebsd.org> wrote:
> on 19/10/2010 00:01 Giovanni Trematerra said the following:
>>
>> Your patch seems just a work around about initial slab size where the
>> keg is backed.
>
> Well, setting aside my confusion with the terminology - yes, the patch is just
> that, and precisely because I only tried to solve that particular problem.
>
>> Having dynamic slab sizes would allow to have the keg backed on a larger slab
>> without going OFFPAGE.
>
> I agree in principle.
> But without seeing code that implements that I can't guess if it would really be
> more efficient or more maintainable, i.e. more useful in general.
> Still a very good idea.
>

Here the patch that was in my mind.
The patch doesn't implement dynamic slab size just allow
to have a multipage slab to back uma_zone objects.
I'm going to work more on the topic "dynamic slab size" soon.
I tested the patch on qemu with -smp 32.
I'm looking for real hw to test the patch on.

here some interesting output:
qemulab# vmstat -z | more
ITEM                   SIZE  LIMIT     USED     FREE      REQ FAIL SLEEP

UMA Kegs:               208,      0,     149,       4,     149,   0,   0
UMA Zones:             4480,      0,     149,       0,     149,   0,   0
UMA Slabs:              568,      0,     836,       4,    1187,   0,   0
UMA RCntSlabs:          568,      0,     202,       1,     202,   0,   0
UMA Hash:               256,      0,       2,      13,       3,   0,   0

qemulab# sysctl kern | grep cpu
kern.ccpu: 0
  <cpu count="32" mask="0xffffffff">0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27,
28, 29, 30, 31</cpu>
kern.smp.cpus: 32
kern.smp.maxcpus: 32

Any feedback will be appreciate.

--
Giovanni Trematerra


==============================================================
diff -r 36572cbc6817 sys/vm/uma_core.c
--- a/sys/vm/uma_core.c	Tue Oct 05 04:49:04 2010 -0400
+++ b/sys/vm/uma_core.c	Mon Nov 01 11:54:38 2010 -0400
@@ -930,27 +930,36 @@ startup_alloc(uma_zone_t zone, int bytes
 {
 	uma_keg_t keg;
 	uma_slab_t tmps;
-
-	keg = zone_first_keg(zone);
+	u_int16_t pages;
+
+	keg   = zone_first_keg(zone);
+	pages = bytes / PAGE_SIZE;
+
+	/* Account for remainder */
+	if ((pages * PAGE_SIZE) < bytes)
+		pages++;
+	KASSERT(pages > 0, ("startup_alloc can't reserve 0 pages\n"));

 	/*
 	 * Check our small startup cache to see if it has pages remaining.
 	 */
 	mtx_lock(&uma_boot_pages_mtx);
-	if ((tmps = LIST_FIRST(&uma_boot_pages)) != NULL) {
-		LIST_REMOVE(tmps, us_link);
+	do {
+		if ((tmps = LIST_FIRST(&uma_boot_pages)) != NULL)
+			LIST_REMOVE(tmps, us_link);
+	} while (--pages && tmps != NULL);
+	if (tmps != NULL) {
 		mtx_unlock(&uma_boot_pages_mtx);
 		*pflag = tmps->us_flags;
 		return (tmps->us_data);
-	}
+	} else if (booted == 0)
+		panic("UMA: Increase vm.boot_pages");
 	mtx_unlock(&uma_boot_pages_mtx);
-	if (booted == 0)
-		panic("UMA: Increase vm.boot_pages");
 	/*
 	 * Now that we've booted reset these users to their real allocator.
 	 */
 #ifdef UMA_MD_SMALL_ALLOC
-	keg->uk_allocf = uma_small_alloc;
+	keg->uk_allocf = (keg->uk_ppera > 1) ? page_alloc : uma_small_alloc;
 #else
 	keg->uk_allocf = page_alloc;
 #endif
@@ -1163,7 +1172,7 @@ keg_small_init(uma_keg_t keg)
 static void
 keg_large_init(uma_keg_t keg)
 {
-	int pages;
+	u_int16_t pages;

 	KASSERT(keg != NULL, ("Keg is null in keg_large_init"));
 	KASSERT((keg->uk_flags & UMA_ZFLAG_CACHEONLY) == 0,
@@ -1177,12 +1186,15 @@ keg_large_init(uma_keg_t keg)

 	keg->uk_ppera = pages;
 	keg->uk_ipers = 1;
+	keg->uk_rsize = keg->uk_size;
+
+	/* We can't do OFFPAGE if we're internal, bail out here. */
+	if (keg->uk_flags & UMA_ZFLAG_INTERNAL)
+		return;

 	keg->uk_flags |= UMA_ZONE_OFFPAGE;
 	if ((keg->uk_flags & UMA_ZONE_VTOSLAB) == 0)
 		keg->uk_flags |= UMA_ZONE_HASH;
-
-	keg->uk_rsize = keg->uk_size;
 }

 static void
@@ -1301,7 +1313,8 @@ keg_ctor(void *mem, int size, void *udat
 #endif
 		if (booted == 0)
 			keg->uk_allocf = startup_alloc;
-	}
+	} else if (booted == 0 && (keg->uk_flags & UMA_ZFLAG_INTERNAL))
+		keg->uk_allocf = startup_alloc;

 	/*
 	 * Initialize keg's lock (shared among zones).
@@ -1330,7 +1343,7 @@ keg_ctor(void *mem, int size, void *udat
 		if (totsize & UMA_ALIGN_PTR)
 			totsize = (totsize & ~UMA_ALIGN_PTR) +
 			    (UMA_ALIGN_PTR + 1);
-		keg->uk_pgoff = UMA_SLAB_SIZE - totsize;
+		keg->uk_pgoff = (UMA_SLAB_SIZE * keg->uk_ppera) - totsize;

 		if (keg->uk_flags & UMA_ZONE_REFCNT)
 			totsize = keg->uk_pgoff + sizeof(struct uma_slab_refcnt)
@@ -1346,7 +1359,7 @@ keg_ctor(void *mem, int size, void *udat
 		 * mathematically possible for all cases, so we make
 		 * sure here anyway.
 		 */
-		if (totsize > UMA_SLAB_SIZE) {
+		if (totsize > UMA_SLAB_SIZE * keg->uk_ppera) {
 			printf("zone %s ipers %d rsize %d size %d\n",
 			    zone->uz_name, keg->uk_ipers, keg->uk_rsize,
 			    keg->uk_size);