Messages in this thread | | | Subject | Re: [RFC] Tagging of vmalloc pages for supporting the pmalloc allocator | From | Igor Stoppa <> | Date | Thu, 3 Aug 2017 18:06:11 +0300 |
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On 03/08/17 17:47, Jerome Glisse wrote: > On Thu, Aug 03, 2017 at 03:55:50PM +0200, Michal Hocko wrote: >> On Thu 03-08-17 15:20:31, Igor Stoppa wrote:
[...]
>>> I am confused about this: if "private2" is a pointer, but when I get an >>> address, I do not even know if the address represents a valid pmalloc >>> page, how can i know when it's ok to dereference "private2"? >> >> because you can make all pages which back vmalloc mappings have vm_area >> pointer set. > > Note that i think this might break some device driver that use vmap() > i think some of them use private field to store device driver specific > informations. But there likely is an unuse field in struct page that > can be use for that.
This increases the unease from my side ... it looks like there is no way to fully understand if a field is really used or not, without having deep intimate knowledge of lots of code that is only marginally involved :-/
Similarly, how would I be able to specify what would be the correct way to decide the member of the union to use for handling the field?
If there were either some sort of non-multiplexed tag/cookie field or a function, that would specify how to treat the various unions, then it would be easier to multiplex the remaining data, according to how the page is used.
-- igor
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