[PATCH] mm/vmalloc: Use batched page requests in bulk-allocator

[PATCH] mm/vmalloc: Use batched page requests in bulk-allocator

[Uladzislau Rezki (Sony)]

In case of simultaneous vmalloc allocations, for example it is 1GB and
12 CPUs my system is able to hit "BUG: soft lockup" for !CONFIG_PREEMPT
kernel.

<snip>
[   62.512621] RIP: 0010:__alloc_pages_bulk+0xa9f/0xbb0
[   62.512628] Code: ff 8b 44 24 48 44 29 f8 83 f8 01 0f 84 ea fe ff ff e9 07 f6 ff ff 48 8b 44 24 60 48 89 28 e9 00 f9 ff ff fb 66 0f 1f 44 00 00 <e9> e8 fd ff ff 65 48 01 51 10 e9 3e fe ff ff 48 8b 44 24 78 4d 89
[   62.512629] RSP: 0018:ffffa7bfc29ffd20 EFLAGS: 00000206
[   62.512631] RAX: 0000000000000200 RBX: ffffcd5405421888 RCX: ffff8c36ffdeb928
[   62.512632] RDX: 0000000000040000 RSI: ffffa896f06b2ff8 RDI: ffffcd5405421880
[   62.512633] RBP: ffffcd5405421880 R08: 000000000000007d R09: ffffffffffffffff
[   62.512634] R10: ffffffff9d63c084 R11: 00000000ffffffff R12: ffff8c373ffaeb80
[   62.512635] R13: ffff8c36ffdf65f8 R14: ffff8c373ffaeb80 R15: 0000000000040000
[   62.512637] FS:  0000000000000000(0000) GS:ffff8c36ffdc0000(0000) knlGS:0000000000000000
[   62.512638] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   62.512639] CR2: 000055c8e2fe8610 CR3: 0000000c13e10000 CR4: 00000000000006e0
[   62.512641] Call Trace:
[   62.512646]  __vmalloc_node_range+0x11c/0x2d0
[   62.512649]  ? full_fit_alloc_test+0x140/0x140 [test_vmalloc]
[   62.512654]  __vmalloc_node+0x4b/0x70
[   62.512656]  ? fix_size_alloc_test+0x44/0x60 [test_vmalloc]
[   62.512659]  fix_size_alloc_test+0x44/0x60 [test_vmalloc]
[   62.512662]  test_func+0xe7/0x1f0 [test_vmalloc]
[   62.512666]  ? fix_align_alloc_test+0x50/0x50 [test_vmalloc]
[   62.512668]  kthread+0x11a/0x140
[   62.512671]  ? set_kthread_struct+0x40/0x40
[   62.512672]  ret_from_fork+0x22/0x30
<snip>

To address this issue invoke a bulk-allocator many times until all pages
are obtained, i.e. do batched page requests adding cond_resched() meanwhile
to reschedule. Batched value is hard-coded and is 100 pages per call.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
---
 mm/vmalloc.c | 32 ++++++++++++++++++++++++++++----
 1 file changed, 28 insertions(+), 4 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index aaad569e8963..01ad46f97365 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2785,10 +2785,34 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
 	 * to fails, fallback to a single page allocator that is
 	 * more permissive.
 	 */
-	if (!order)
-		nr_allocated = alloc_pages_bulk_array_node(
-			gfp, nid, nr_pages, pages);
-	else
+	if (!order) {
+		while (nr_allocated < nr_pages) {
+			int nr, nr_pages_request;
+
+			/*
+			 * A maximum allowed request is hard-coded and is 100
+			 * pages per call. That is done in order to prevent a
+			 * long preemption off scenario in the bulk-allocator
+			 * so the range is [1:100].
+			 */
+			nr_pages_request = min(100, (int)(nr_pages - nr_allocated));
+
+			nr = alloc_pages_bulk_array_node(gfp, nid,
+				nr_pages_request, pages + nr_allocated);
+
+			nr_allocated += nr;
+
+			if (gfpflags_allow_blocking(gfp))
+				cond_resched();
+
+			/*
+			 * If zero or pages were obtained partly,
+			 * fallback to a single page allocator.
+			 */
+			if (nr != nr_pages_request)
+				break;
+		}
+	} else
 		/*
 		 * Compound pages required for remap_vmalloc_page if
 		 * high-order pages.
-- 
2.20.1

Re: [PATCH] mm/vmalloc: Use batched page requests in bulk-allocator

[Matthew Wilcox]

On Mon, Jul 05, 2021 at 04:55:47PM +0200, Uladzislau Rezki (Sony) wrote:
> +			if (gfpflags_allow_blocking(gfp))
> +				cond_resched();

How does one call vmalloc() with gfp flags that _don't_ allow blocking?
They have to allow a GFP_KERNEL allocation of the page tables.
So I think this should be an unconditional cond_resched().

Re: [PATCH] mm/vmalloc: Use batched page requests in bulk-allocator

[Uladzislau Rezki]

> On Mon, Jul 05, 2021 at 04:55:47PM +0200, Uladzislau Rezki (Sony) wrote:
> > +			if (gfpflags_allow_blocking(gfp))
> > +				cond_resched();
> 
> How does one call vmalloc() with gfp flags that _don't_ allow blocking?
> They have to allow a GFP_KERNEL allocation of the page tables.
> So I think this should be an unconditional cond_resched().
Historically it is there. I decided to align with below code. But i agree
vmalloc is sleepable anyway, so blocking is supposed.

OK, i will respin and send out two patches. 

--
Vlad Rezki