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

[Baoquan He <bhe@redhat.com>]

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?
If yes, I have one patch queued to fix it in another way which I have
been trying to take in mind.

Thanks
Baoquan