Messages in this thread | | | From | Christophe Leroy <> | Subject | Re: [PATCH] hugetlb: simplify hugetlb handling in follow_page_mask | Date | Sat, 3 Sep 2022 07:07:44 +0000 |
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+Resending with valid powerpc list address
Le 02/09/2022 à 20:52, David Hildenbrand a écrit : >>>> Adding Christophe on Cc: >>>> >>>> Christophe do you know if is_hugepd is true for all hugetlb entries, not >>>> just hugepd?
is_hugepd() is true if and only if the directory entry points to a huge page directory and not to the normal lower level directory.
As far as I understand if the directory entry is not pointing to any lower directory but is a huge page entry, pXd_leaf() is true.
>>>> >>>> On systems without hugepd entries, I guess ptdump skips all hugetlb entries. >>>> Sigh!
As far as I can see, ptdump_pXd_entry() handles the pXd_leaf() case.
>>> >>> IIUC, the idea of ptdump_walk_pgd() is to dump page tables even outside >>> VMAs (for debugging purposes?). >>> >>> I cannot convince myself that that's a good idea when only holding the >>> mmap lock in read mode, because we can just see page tables getting >>> freed concurrently e.g., during concurrent munmap() ... while holding >>> the mmap lock in read we may only walk inside VMA boundaries. >>> >>> That then raises the questions if we're only calling this on special MMs >>> (e.g., init_mm) whereby we cannot really see concurrent munmap() and >>> where we shouldn't have hugetlb mappings or hugepd entries.
At least on powerpc, PTDUMP handles only init_mm.
Hugepage are used at least on powerpc 8xx for linear memory mapping, see
commit 34536d780683 ("powerpc/8xx: Add a function to early map kernel via huge pages") commit cf209951fa7f ("powerpc/8xx: Map linear memory with huge pages")
hugepds may also be used in the future to use huge pages for vmap and vmalloc, see commit a6a8f7c4aa7e ("powerpc/8xx: add support for huge pages on VMAP and VMALLOC")
As far as I know, ppc64 also use huge pages for VMAP and VMALLOC, see
commit d909f9109c30 ("powerpc/64s/radix: Enable HAVE_ARCH_HUGE_VMAP") commit 8abddd968a30 ("powerpc/64s/radix: Enable huge vmalloc mappings")
Christophe | |