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

Michal Hocko
2022-08-03T15:05:25Z

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.

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

Any reference?

--
Michal Hocko
SUSE Labs