On Wed, May 6, 2015 at 1:05 PM, Dan Williams <dan.j.williams(a)intel.com> wrote:
In preparation for converting struct bio_vec to carry a __pfn_t
of struct page.
This change is prompted by the desire to add in-kernel DMA support
(O_DIRECT, hierarchical storage, RDMA, etc) for persistent memory which
lacks struct page coverage.
1/ Provide struct page coverage for persistent memory in DRAM. The
expectation is that persistent memory capacities make this untenable
in the long term.
2/ Provide struct page coverage for persistent memory with persistent
memory. While persistent memory may have near DRAM performance
characteristics it may not have the same write-endurance of DRAM.
Given the update frequency of struct page objects it may not be
suitable for persistent memory.
3/ Dynamically allocate struct page. This appears to be on the order
of the complexity of converting code paths to use __pfn_t references
instead of struct page, and the amount of setup required to establish
a valid struct page reference is mostly wasted when the only usage in
the block stack is to perform a page_to_pfn() conversion for
dma-mapping. Instances of kmap() / kmap_atomic() usage appear to be
the only occasions in the block stack where struct page is
non-trivially used. A new kmap_atomic_pfn_t() is proposed to handle
Generated with the following semantic patch:
// bv_page.cocci: convert usage of ->bv_page to use set/get helpers
// usage: make coccicheck COCCI=bv_page.cocci MODE=patch
Now that it looks like this patchset can move forward, what do about
this one? Run the Coccinelle script late in the merge window to catch
all the new bv_page usages targeted for 4.2-rc1?