From: Hyeonggon Yoo <42.hyeyoo@gmail.com>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Baoquan He <bhe@redhat.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
akpm@linux-foundation.org, hch@lst.de, cl@linux.com,
John.p.donnelly@oracle.com, kexec@lists.infradead.org,
stable@vger.kernel.org, Pekka Enberg <penberg@kernel.org>,
David Rientjes <rientjes@google.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>
Subject: Re: [PATCH v3 5/5] mm/slub: do not create dma-kmalloc if no managed pages in DMA zone
Date: Wed, 15 Dec 2021 07:03:35 +0000 [thread overview]
Message-ID: <20211215070335.GA1165926@odroid> (raw)
In-Reply-To: <20211215044818.GB1097530@odroid>
On Wed, Dec 15, 2021 at 04:48:26AM +0000, Hyeonggon Yoo wrote:
>
> Hello Baoquan and Vlastimil.
>
> I'm not sure allowing ZONE_DMA32 for kdump kernel is nice way to solve
> this problem. Devices that requires ZONE_DMA is rare but we still
> support them.
>
> If we allow ZONE_DMA32 for ZONE_DMA in kdump kernels,
> the problem will be hard to find.
>
Sorry, I sometimes forget validating my english writing :(
What I meant:
I'm not sure that allocating from ZONE_DMA32 instead of ZONE_DMA
for kdump kernel is nice way to solve this problem.
Devices that requires ZONE_DMA memory is rare but we still support them.
If we use ZONE_DMA32 memory instead of ZONE_DMA in kdump kernels,
It will be hard to the problem when we use devices that can use only
ZONE_DMA memory.
> What about one of those?:
>
> 1) Do not call warn_alloc in page allocator if will always fail
> to allocate ZONE_DMA pages.
>
>
> 2) let's check all callers of kmalloc with GFP_DMA
> if they really need GFP_DMA flag and replace those by DMA API or
> just remove GFP_DMA from kmalloc()
>
> 3) Drop support for allocating DMA memory from slab allocator
> (as Christoph Hellwig said) and convert them to use DMA32
(as Christoph Hellwig said) and convert them to use *DMA API*
> and see what happens
>
> Thanks,
> Hyeonggon.
>
> > >>
> > >> Maybe the function get_capabilities() want to allocate memory
> > >> even if it's not from DMA zone, but other callers will not expect that.
> > >
> > > Yeah, I have the same guess too for get_capabilities(), not sure about other
> > > callers. Or, as ChristophL and ChristophH said(Sorry, not sure if this is
> > > the right way to call people when the first name is the same. Correct me if
> > > it's wrong), any buffer requested from kmalloc can be used by device driver.
> > > Means device enforces getting memory inside addressing limit for those
> > > DMA transferring buffer which is usually large, Megabytes level with
> > > vmalloc() or alloc_pages(), but doesn't care about this kind of small
> > > piece buffer memory allocated with kmalloc()? Just a guess, please tell
> > > a counter example if anyone happens to know, it could be easy.
> > >
> > >
> > >>
> > >> > kmalloc_caches[KMALLOC_DMA][i] = create_kmalloc_cache(
> > >> > kmalloc_info[i].name[KMALLOC_DMA],
> > >> > kmalloc_info[i].size,
> > >> > --
> > >> > 2.17.2
> > >> >
> > >> >
> > >>
> > >
> >
next prev parent reply other threads:[~2021-12-15 7:03 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20211213122712.23805-1-bhe@redhat.com>
2021-12-13 12:27 ` [PATCH v3 3/5] mm_zone: add function to check if managed dma zone exists Baoquan He
2021-12-13 14:22 ` john.p.donnelly
2021-12-16 10:52 ` David Hildenbrand
2021-12-13 12:27 ` [PATCH v3 4/5] dma/pool: create dma atomic pool only if dma zone has managed pages Baoquan He
2021-12-13 14:23 ` john.p.donnelly
2021-12-13 12:27 ` [PATCH v3 5/5] mm/slub: do not create dma-kmalloc if no managed pages in DMA zone Baoquan He
2021-12-13 13:43 ` Hyeonggon Yoo
2021-12-14 5:32 ` Baoquan He
2021-12-14 10:09 ` Vlastimil Babka
2021-12-14 10:28 ` Christoph Lameter
2021-12-15 4:48 ` Hyeonggon Yoo
2021-12-15 7:03 ` Hyeonggon Yoo [this message]
2021-12-15 7:27 ` Christoph Hellwig
2021-12-15 10:34 ` Vlastimil Babka
2021-12-15 11:51 ` David Laight
2021-12-15 13:41 ` Baoquan He
2021-12-17 11:38 ` Hyeonggon Yoo
2021-12-20 7:32 ` Baoquan He
2022-01-07 11:56 ` Hyeonggon Yoo
2021-12-15 14:42 ` Baoquan He
2021-12-15 10:08 ` Baoquan He
2021-12-17 11:38 ` Hyeonggon Yoo
2021-12-21 8:56 ` Christoph Hellwig
2021-12-22 12:37 ` Hyeonggon Yoo
2021-12-23 8:52 ` Christoph Hellwig
2021-12-13 14:24 ` john.p.donnelly
2021-12-14 16:31 ` Christoph Hellwig
2021-12-14 17:07 ` john.p.donnelly
2021-12-15 7:27 ` Christoph Hellwig
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