On Fri, Jul 27, 2018 at 09:23:30AM -0400, Tony Battersby wrote:
> On 07/26/2018 08:07 PM, Matthew Wilcox wrote:
> > If you're up for more major surgery, then I think we can put all the
> > information currently stored in dma_page into struct page. Something
> > like this:
> >
> > +++ b/include/linux/mm_types.h
> > @@ -152,6 +152,12 @@ struct page {
> > unsigned long hmm_data;
> > unsigned long _zd_pad_1; /* uses mapping */
> > };
> > + struct { /* dma_pool pages */
> > + struct list_head dma_list;
> > + unsigned short in_use;
> > + unsigned short offset;
> > + dma_addr_t dma;
> > + };
> >
> > /** @rcu_head: You can use this to free a page by RCU. */
> > struct rcu_head rcu_head;
> >
> > page_list -> dma_list
> > vaddr goes away (page_to_virt() exists)
> > dma -> dma
> > in_use and offset shrink from 4 bytes to 2.
> >
> > Some 32-bit systems have a 64-bit dma_addr_t, and on those systems,
> > this will be 8 + 2 + 2 + 8 = 20 bytes. On 64-bit systems, it'll be
> > 16 + 2 + 2 + 4 bytes of padding + 8 = 32 bytes (we have 40 available).
> >
> >
> offset at least needs more bits, since allocations can be multi-page.
Ah, rats. That means we have to use the mapcount union too:
+++ b/include/linux/mm_types.h
@@ -152,6 +152,11 @@ struct page {
unsigned long hmm_data;
unsigned long _zd_pad_1; /* uses mapping */
};
+ struct { /* dma_pool pages */
+ struct list_head dma_list;
+ unsigned int dma_in_use;
+ dma_addr_t dma;
+ };
/** @rcu_head: You can use this to free a page by RCU. */
struct rcu_head rcu_head;
@@ -174,6 +179,7 @@ struct page {
unsigned int active; /* SLAB */
int units; /* SLOB */
+ unsigned int dma_offset; /* dma_pool */
};
/* Usage count. *DO NOT USE DIRECTLY*. See page_ref.h */
> See the following from mpt3sas:
>
> cat /sys/devices/pci0000:80/0000:80:07.0/0000:85:00.0/pools
> (manually cleaned up column alignment)
> poolinfo - 0.1
> reply_post_free_array pool 1 21 192 1
> reply_free pool 1 1 41728 1
> reply pool 1 1 1335296 1
> sense pool 1 1 970272 1
> chain pool 373959 386048 128 12064
> reply_post_free pool 12 12 166528 12
> ^size^
Wow, that's a pretty weird way to use the dmapool. It'd be more efficient
to just call dma_alloc_coherent() directly.
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