lkml.org 
[lkml]   [2015]   [May]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: "Directly mapped persistent memory page cache"
From
On Sun, May 10, 2015 at 2:46 AM, Ingo Molnar <mingo@kernel.org> wrote:
>
> * Dan Williams <dan.j.williams@intel.com> wrote:
>
>> > "Directly mapped pmem integrated into the page cache":
>> > ------------------------------------------------------
>
>> Nice, I think it makes sense as an area that gets reserved at file
>> system creation time. You are not proposing that this gets
>> automatically reserved at the device level, right? [...]
>
> Well, it's most practical if the device does it automatically (the
> layout is determined prior filesystem creation), and the filesystem
> does not necessarily have to be aware of it - but obviously as a user
> opt-in.
>

Hmm, my only hesitation is that the raw size of a pmem device is
visible outside of Linux (UEFI/BIOS other OSes, etc). What about a
simple layered block-device that fronts a raw pmem device? It can
store a small superblock signature and then reserve / init the struct
page space. This is where we can use the __pfn_t flags that Linus
suggested. Whereas the raw device ->direct_access() returns __pfn_t
values with a 'PFN_DEV' flag indicating originating from
device-memory, a ->direct_access() on this struct-page-provider-device
yields __pfn_t's with 'PFN_DEV | PFN_MAPPED' indicating that
__pfn_t_to_page() can attempt to lookup the page in a device-specific
manner (similar to how kmap_atomic_pfn_t is implemented in the
'evacuate struct page from the block layer' patch set).


\
 
 \ /
  Last update: 2015-05-10 19:41    [W:0.063 / U:20.416 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site