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Message-Id: <1402609691-13950-9-git-send-email-n-horiguchi@ah.jp.nec.com> Date: Thu, 12 Jun 2014 17:48:08 -0400 From: Naoya Horiguchi <n-horiguchi@...jp.nec.com> To: linux-mm@...ck.org Cc: Dave Hansen <dave.hansen@...el.com>, Andrew Morton <akpm@...ux-foundation.org>, Hugh Dickins <hughd@...gle.com>, "Kirill A. Shutemov" <kirill@...temov.name>, linux-kernel@...r.kernel.org Subject: [PATCH -mm v2 08/11] pagewalk: update comment on walk_page_range() Rewriting common code of page table walker has been done, so this patch updates the comment on walk_page_range() for the future development. Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com> --- mm/pagewalk.c | 55 +++++++++++++++++++++++++++---------------------------- 1 file changed, 27 insertions(+), 28 deletions(-) diff --git mmotm-2014-05-21-16-57.orig/mm/pagewalk.c mmotm-2014-05-21-16-57/mm/pagewalk.c index b46c8882c643..626a80d4d9dd 100644 --- mmotm-2014-05-21-16-57.orig/mm/pagewalk.c +++ mmotm-2014-05-21-16-57/mm/pagewalk.c @@ -253,39 +253,38 @@ static int __walk_page_range(unsigned long start, unsigned long end, * walk_page_range - walk page table with caller specific callbacks * * Recursively walk the page table tree of the process represented by - * @walk->mm within the virtual address range [@start, @end). In walking, - * we can call caller-specific callback functions against each entry. + * @walk->mm within the virtual address range [@start, @end). During walking, + * we can call caller-specific callback functions against each leaf entry. * * Before starting to walk page table, some callers want to check whether - * they really want to walk over the vma (for example by checking vm_flags.) - * walk_page_test() and @walk->test_walk() do that check. + * they really want to walk over the current vma, typically by checking + * its vm_flags. walk_page_test() and @walk->test_walk() are used for this + * purpose. * - * If any callback returns a non-zero value, the page table walk is aborted - * immediately and the return value is propagated back to the caller. - * Note that the meaning of the positive returned value can be defined - * by the caller for its own purpose. + * Currently we have three types of possible leaf enties, pte (for normal + * pages,) pmd (for thps,) and hugetlb. We handle these three with pte_entry(), + * pmd_entry(), and hugetlb_entry(), respectively. + * If you don't set any function to some of these callbacks, the associated + * entries/pages are ignored. + * The return values of these three callbacks are commonly defined like below: + * - 0 : succeeded to handle the current entry, and if you don't reach the + * end address yet, continue to walk. + * - >0 : succeeded to handle the current entry, and return to the caller + * with caller specific value. + * - <0 : failed to handle the current entry, and return to the caller + * with error code. + * We can set the same function to different callbacks, where @walk->size + * should be helpful to know the type of entry in callbacks. * - * If the caller defines multiple callbacks in different levels, the - * callbacks are called in depth-first manner. It could happen that - * multiple callbacks are called on a address. For example if some caller - * defines test_walk(), pmd_entry(), and pte_entry(), then callbacks are - * called in the order of test_walk(), pmd_entry(), and pte_entry(). - * If you don't want to go down to lower level at some point and move to - * the next entry in the same level, you set @walk->skip to 1. - * For example if you succeed to handle some pmd entry as trans_huge entry, - * you need not call walk_pte_range() any more, so set it to avoid that. - * We can't determine whether to go down to lower level with the return - * value of the callback, because the whole range of return values (0, >0, - * and <0) are used up for other meanings. + * struct mm_walk keeps current values of some common data like vma and pmd, + * which are useful for the access from callbacks. If you want to pass some + * caller-specific data to callbacks, @walk->private should be helpful. * - * Each callback can access to the vma over which it is doing page table - * walk right now via @walk->vma. @walk->vma is set to NULL in walking - * outside a vma. If you want to access to some caller-specific data from - * callbacks, @walk->private should be helpful. - * - * The callers should hold @walk->mm->mmap_sem. Note that the lower level - * iterators can take page table lock in lowest level iteration and/or - * in split_huge_page_pmd(). + * Locking: + * Callers of walk_page_range() and walk_page_vma() should hold + * @walk->mm->mmap_sem, because these function traverse vma list and/or + * access to vma's data. And page table lock is held during running + * pmd_entry(), pte_entry(), and hugetlb_entry(). */ int walk_page_range(unsigned long start, unsigned long end, struct mm_walk *walk) -- 1.9.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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