Messages in this thread | | | Subject | Re: [RFC] Tagging of vmalloc pages for supporting the pmalloc allocator | From | Igor Stoppa <> | Date | Thu, 3 Aug 2017 15:20:31 +0300 |
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On 03/08/17 14:48, Michal Hocko wrote: > On Thu 03-08-17 13:11:45, Igor Stoppa wrote: >> On 02/08/17 20:08, Jerome Glisse wrote: >>> On Wed, Aug 02, 2017 at 06:14:28PM +0300, Igor Stoppa wrote:
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>>>> from include/linux/mm_types.h: >>>> >>>> struct page { >>>> ... >>>> union { >>>> unsigned long private; /* Mapping-private opaque data: >>>> * usually used for buffer_heads >>>> * if PagePrivate set; used for >>>> * swp_entry_t if PageSwapCache; >>>> * indicates order in the buddy >>>> * system if PG_buddy is set. >>>> */
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>> If the "Mapping-private" was dropped or somehow connected exclusively to >> the cases listed in the comment, then I think it would be more clear >> that the comment needs to be intended as related to mapping in certain >> cases only. >> But it is otherwise ok to use the "private" field for whatever purpose >> it might be suitable, as long as it is not already in use. > > I would recommend adding a new field into the enum...
s/enum/union/ ?
If not, I am not sure what is the enum that you are talking about.
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>> But, to reply more specifically to your advice, yes, I think I could add >> a flag to vm_struct and then retrieve its value, for the address being >> processed, by passing through find_vm_area(). > > ... and you can store vm_struct pointer to the struct page there
"there" as in the new field of the union? btw, what would be a meaningful name, since "private" is already taken?
For simplicity, I'll use, for now, "private2"
> and you> won't need to do the slow find_vm_area. I haven't checked very closely > but this should be possible in principle. I guess other callers might > benefit from this as well.
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"?
Since it's just another field in a union, it can actually contain a value that should be interpreted as some other field, right?
-- thanks, igor
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