Messages in this thread | | | Subject | Re: [PATCH 1/3] powerpc/32: Fix hugepage allocation on 8xx at hint address | From | "Aneesh Kumar K.V" <> | Date | Tue, 16 Jan 2018 22:13:39 +0530 |
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On 01/16/2018 10:01 PM, Christophe LEROY wrote: > > > Le 16/01/2018 à 16:49, Aneesh Kumar K.V a écrit : >> Christophe Leroy <christophe.leroy@c-s.fr> writes: >> >>> When an app has some regular pages allocated (e.g. see below) and tries >>> to mmap() a huge page at a hint address covered by the same PMD entry, >>> the kernel accepts the hint allthough the 8xx cannot handle different >>> page sizes in the same PMD entry. >> >> >> So that is a bug in get_unmapped_area function that you are using and >> you want to fix that by using the slice code. Can you describe here what >> the allocation restrictions are w.r.t 8xx? Do they have segments and >> base page size like hash64? > > I don't think it is a bug in get_unmapped_area() that is used by > default. It is that some HW do support mixing any page size in the same > page table (eg BOOK3E ?), but the 8xx doesn't. > In the 8xx, the page size is defined in the PGD entry, then all pages > defined in a given page table pointed by a PGD entry have the same size. > > So it is similar to segments if you consider each PGD entry as a kind of > segment >
so IIUC, hugepd format encodes the page size details and that require us to ensure that all the address range mapped at that hupge_pd entry is of same page size? Hence we want to avoid mmap handing over an address in that range when we already have a hugetlb mapping in that range?
-aneesh
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