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Patch series "mm/gup: Unify hugetlb, speed up thp", v4. Hugetlb has a special path for slow gup that follow_page_mask() is actually skipped completely along with faultin_page(). It's not only confusing, but also duplicating a lot of logics that generic gup already has, making hugetlb slightly special. This patchset tries to dedup the logic, by first touching up the slow gup code to be able to handle hugetlb pages correctly with the current follow page and faultin routines (where we're mostly there.. due to 10 years ago we did try to optimize thp, but half way done; more below), then at the last patch drop the special path, then the hugetlb gup will always go the generic routine too via faultin_page(). Note that hugetlb is still special for gup, mostly due to the pgtable walking (hugetlb_walk()) that we rely on which is currently per-arch. But this is still one small step forward, and the diffstat might be a proof too that this might be worthwhile. Then for the "speed up thp" side: as a side effect, when I'm looking at the chunk of code, I found that thp support is actually partially done. It doesn't mean that thp won't work for gup, but as long as **pages pointer passed over, the optimization will be skipped too. Patch 6 should address that, so for thp we now get full speed gup. For a quick number, "chrt -f 1 ./gup_test -m 512 -t -L -n 1024 -r 10" gives me 13992.50us -> 378.50us. Gup_test is an extreme case, but just to show how it affects thp gups. This patch (of 8): Firstly, the no_page_table() is meaningless for hugetlb which is a no-op there, because a hugetlb page always satisfies: - vma_is_anonymous() == false - vma->vm_ops->fault != NULL So we can already safely remove it in hugetlb_follow_page_mask(), alongside with the page* variable. Meanwhile, what we do in follow_hugetlb_page() actually makes sense for a dump: we try to fault in the page only if the page cache is already allocated. Let's do the same here for follow_page_mask() on hugetlb. It should so far has zero effect on real dumps, because that still goes into follow_hugetlb_page(). But this may start to influence a bit on follow_page() users who mimics a "dump page" scenario, but hopefully in a good way. This also paves way for unifying the hugetlb gup-slow. Link: https://lkml.kernel.org/r/20230628215310.73782-1-peterx@redhat.com Link: https://lkml.kernel.org/r/20230628215310.73782-2-peterx@redhat.com Signed-off-by: Peter Xu <peterx@redhat.com> Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com> Reviewed-by: David Hildenbrand <david@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: James Houghton <jthoughton@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Kirill A . Shutemov <kirill@shutemov.name> Cc: Lorenzo Stoakes <lstoakes@gmail.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Mike Rapoport (IBM) <rppt@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Yang Shi <shy828301@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.