Re: Fwd: vmalloc error: btrfs-delalloc btrfs_work_helper [btrfs] in kernel 6.3.x

[Uladzislau Rezki]

> Hi,
> 
> I notice a regression report on Bugzilla [1]. Quoting from it:
> 
> > after updating from 6.2.x to 6.3.x, vmalloc error messages started to appear in the dmesg
> > 
> > 
> > 
> > # free 
> >                total        used        free      shared  buff/cache   available
> > Mem:        16183724     1473068      205664       33472    14504992    14335700
> > Swap:       16777212      703596    16073616
> > 
> > 
> > (zswap enabled)
> 
> See bugzilla for the full thread and attached dmesg.
> 
> On the report, the reporter can't perform the required bisection,
> unfortunately.
> 
> Anyway, I'm adding it to regzbot:
> 
> #regzbot introduced: v6.2..v6.3 https://bugzilla.kernel.org/show_bug.cgi?id=217466
> #regzbot title: btrfs_work_helper dealloc error in v6.3.x
> 
> Thanks.
> 
> [1]: https://bugzilla.kernel.org/show_bug.cgi?id=217466
> 
According to dmesg output from the bugzilla, the vmalloc tries to
allocate high order pages: 1 << 9. Since it fails to get a order-9 page
you get the warning:

<snip>
	if (area->nr_pages != nr_small_pages) {
		/* vm_area_alloc_pages() can also fail due to a fatal signal */
		if (!fatal_signal_pending(current))
			warn_alloc(gfp_mask, NULL,
				"vmalloc error: size %lu, page order %u, failed to allocate pages",
				area->nr_pages * PAGE_SIZE, page_order);
		goto fail;
	}
<snip>

and it fails.

If the __GFP_NOFAIL is passed, the vm_area_alloc_pages() function switches
to allocate 0-order pages instead. I think the fix is to call the
kvmalloc_node() with __GFP_NOFAIL flag.

--
Uladzislau Rezki