Re: [PATCH] dma/pool: do not complain if DMA pool is not allocated

[Michal Hocko]

On Wed 03-08-22 23:32:03, Baoquan He wrote:
> On 08/03/22 at 05:05pm, Michal Hocko wrote:
> > On Wed 03-08-22 22:59:26, Baoquan He wrote:
> > > On 08/03/22 at 11:52am, Michal Hocko wrote:
> > > > On Fri 25-03-22 17:54:33, Michal Hocko wrote:
> > > > > On Fri 25-03-22 17:48:56, Christoph Hellwig wrote:
> > > > > > On Fri, Mar 25, 2022 at 01:58:42PM +0100, Michal Hocko wrote:
> > > > > > > Dang, I have just realized that I have misread the boot log and it has
> > > > > > > turned out that a674e48c5443 is covering my situation because the
> > > > > > > allocation failure message says:
> > > > > > >
> > > > > > > Node 0 DMA free:0kB boost:0kB min:0kB low:0kB high:0kB reserved_highatomic:0KB active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB present:636kB managed:0kB mlocked:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
> > > > > > 
> > > > > > As in your report is from a kernel that does not have a674e48c5443
> > > > > > yet?
> > > > > 
> > > > > yes. I just mixed up the early boot messages and thought that DMA zone
> > > > > ended up with a single page. That message was saying something else
> > > > > though.
> > > > 
> > > > OK, so I have another machine spewing this warning. Still on an older
> > > > kernel but I do not think the current upstream would be any different in
> > > > that regards. This time the DMA zone is populated and consumed from
> > > > large part and the pool size request is just too large for it:
> > > > 
> > > > [   14.017417][    T1] swapper/0: page allocation failure: order:10, mode:0xcc1(GFP_KERNEL|GFP_DMA), nodemask=(null),cpuset=/,mems_allowed=0-7
> > > > [   14.017429][    T1] CPU: 4 PID: 1 Comm: swapper/0 Not tainted 5.14.21-150400.22-default #1 SLE15-SP4 0b6a6578ade2de5c4a0b916095dff44f76ef1704
> > > > [   14.017434][    T1] Hardware name: XXXX
> > > > [   14.017437][    T1] Call Trace:
> > > > [   14.017444][    T1]  <TASK>
> > > > [   14.017449][    T1]  dump_stack_lvl+0x45/0x57
> > > > [   14.017469][    T1]  warn_alloc+0xfe/0x160
> > > > [   14.017490][    T1]  __alloc_pages_slowpath.constprop.112+0xc27/0xc60
> > > > [   14.017497][    T1]  ? rdinit_setup+0x2b/0x2b
> > > > [   14.017509][    T1]  ? rdinit_setup+0x2b/0x2b
> > > > [   14.017512][    T1]  __alloc_pages+0x2d5/0x320
> > > > [   14.017517][    T1]  alloc_page_interleave+0xf/0x70
> > > > [   14.017531][    T1]  atomic_pool_expand+0x4a/0x200
> > > > [   14.017541][    T1]  ? rdinit_setup+0x2b/0x2b
> > > > [   14.017544][    T1]  __dma_atomic_pool_init+0x44/0x90
> > > > [   14.017556][    T1]  dma_atomic_pool_init+0xad/0x13f
> > > > [   14.017560][    T1]  ? __dma_atomic_pool_init+0x90/0x90
> > > > [   14.017562][    T1]  do_one_initcall+0x41/0x200
> > > > [   14.017581][    T1]  kernel_init_freeable+0x236/0x298
> > > > [   14.017589][    T1]  ? rest_init+0xd0/0xd0
> > > > [   14.017596][    T1]  kernel_init+0x16/0x120
> > > > [   14.017599][    T1]  ret_from_fork+0x22/0x30
> > > > [   14.017604][    T1]  </TASK>
> > > > [...]
> > > > [   14.018026][    T1] Node 0 DMA free:160kB boost:0kB min:0kB low:0kB high:0kB reserved_highatomic:0KB active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB present:15996kB managed:15360kB mlocked:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
> > > > [   14.018035][    T1] lowmem_reserve[]: 0 0 0 0 0
> > > > [   14.018339][    T1] Node 0 DMA: 0*4kB 0*8kB 0*16kB 1*32kB (U) 0*64kB 1*128kB (U) 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 160kB
> > > > 
> > > > So the DMA zone has only 160kB free while the pool would like to use 4MB
> > > > of it which obviously fails. I haven't tried to check who is consuming
> > > > the DMA zone memory and why but this shouldn't be all that important
> > > > because the pool clearly cannot allocate and there is not much the
> > > > user/admin can do about that. Well, the pool could be explicitly
> > > > requested smaller but is that really what we expect them to do?
> > > >   
> > > > > > > I thought there are only few pages in the managed by the DMA zone. This
> > > > > > > is still theoretically possible so I think __GFP_NOWARN makes sense here
> > > > > > > but it would require to change the patch description.
> > > > > > > 
> > > > > > > Is this really worth it?
> > > > > > 
> > > > > > In general I think for kernels where we need the pool and can't allocate
> > > > > > it, a warning is very useful.  We just shouldn't spew it when there is
> > > > > > no need for the pool to start with.
> > > > > 
> > > > > Well, do we have any way to find that out during early boot?
> > > > 
> > > > Thinking about it. We should get a warning when the actual allocation
> > > > from the pool fails no? That would be more useful information than the
> > > > pre-allocation failure when it is not really clear whether anybody is
> > > > ever going to consume it.
> > > 
> > > Hi Michal,
> > > 
> > > You haven't told on which ARCH you met this issue, is it x86_64?
> > 
> > yes x86_64, so a small 16MB DMA zone.
> 
> Yeah, the 16M DMA zone is redicilous and exists only for hardly seen
> ISA-style devices support. Haven't prepared the log well.

Agreed on that! I would essentially suggest to completely ignore pool
pre-allocation failures for the small DMA zone. There is barely anything
to be ever consuming it.

Unfortunately generic kernels cannot really know there is any
crippled device without some code to some checking early boot (and I am
not even sure this would be sufficient).

> >From 0b32b4c441f9e28bbda06eefbd14c25d00924830 Mon Sep 17 00:00:00 2001
> From: Baoquan He <bhe@xxxxxxxxxx>
> Date: Wed, 6 Jul 2022 15:26:15 +0800
> Subject: [PATCH] x86, 64: let zone DMA cover low 4G if no ISA-style devices
> Content-type: text/plain
> 
> It doesn't make sense to let the rare legacy ISA-style devies
> drag x86_64 to have a tiny zone DMA of 16M which cause many
> troubles.
> 
> Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
> ---
>  arch/x86/Kconfig   | 1 -
>  arch/x86/mm/init.c | 5 ++++-
>  2 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 5aa4c2ecf5c7..93af781f9445 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -2761,7 +2761,6 @@ config ISA_BUS
>  # x86_64 have no ISA slots, but can have ISA-style DMA.
>  config ISA_DMA_API
>  	bool "ISA-style DMA support" if (X86_64 && EXPERT)
> -	default y
>  	help
>  	  Enables ISA-style DMA support for devices requiring such controllers.
>  	  If unsure, say Y.
> diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
> index 82a042c03824..c9ffb38dcc6a 100644
> --- a/arch/x86/mm/init.c
> +++ b/arch/x86/mm/init.c
> @@ -1024,9 +1024,12 @@ void __init zone_sizes_init(void)
>  
>  	memset(max_zone_pfns, 0, sizeof(max_zone_pfns));
>  
> -#ifdef CONFIG_ZONE_DMA
> +#if defined(CONFIG_ZONE_DMA) && defined(CONFIG_ISA_DMA_API)
>  	max_zone_pfns[ZONE_DMA]		= min(MAX_DMA_PFN, max_low_pfn);
> +#else
> +	max_zone_pfns[ZONE_DMA]		= min(MAX_DMA32_PFN, max_low_pfn);
>  #endif
> +
>  #ifdef CONFIG_ZONE_DMA32
>  	max_zone_pfns[ZONE_DMA32]	= min(MAX_DMA32_PFN, max_low_pfn);
>  #endif

I would rather see the zone go away completley and free up the slot in
page flags.  This seems like a hack to have two zones representing the
same physical memory range.

This also mostly papers over this particular problem by allocating
allocating two pools for the same range.

-- 
Michal Hocko
SUSE Labs