From: Hugh Dickins Date: Tue, 22 Sep 2009 00:03:26 +0000 (-0700) Subject: mm: FOLL_DUMP replace FOLL_ANON X-Git-Tag: firefly_0821_release~12772 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=8e4b9a60718970bbc02dfd3abd0b956ab65af231;p=firefly-linux-kernel-4.4.55.git mm: FOLL_DUMP replace FOLL_ANON The "FOLL_ANON optimization" and its use_zero_page() test have caused confusion and bugs: why does it test VM_SHARED? for the very good but unsatisfying reason that VMware crashed without. As we look to maybe reinstating anonymous use of the ZERO_PAGE, we need to sort this out. Easily done: it's silly for __get_user_pages() and follow_page() to be guessing whether it's safe to assume that they're being used for a coredump (which can take a shortcut snapshot where other uses must handle a fault) - just tell them with GUP_FLAGS_DUMP and FOLL_DUMP. get_dump_page() doesn't even want a ZERO_PAGE: an error suits fine. Signed-off-by: Hugh Dickins Acked-by: Rik van Riel Acked-by: Mel Gorman Reviewed-by: Minchan Kim Cc: KAMEZAWA Hiroyuki Cc: KOSAKI Motohiro Cc: Nick Piggin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/include/linux/mm.h b/include/linux/mm.h index e41795bba95d..45ee5b5a343d 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1231,7 +1231,7 @@ struct page *follow_page(struct vm_area_struct *, unsigned long address, #define FOLL_WRITE 0x01 /* check pte is writable */ #define FOLL_TOUCH 0x02 /* mark page accessed */ #define FOLL_GET 0x04 /* do get_page on page */ -#define FOLL_ANON 0x08 /* give ZERO_PAGE if no pgtable */ +#define FOLL_DUMP 0x08 /* give error on hole if it would be zero */ typedef int (*pte_fn_t)(pte_t *pte, pgtable_t token, unsigned long addr, void *data); diff --git a/mm/internal.h b/mm/internal.h index 166765cd58d6..d41475078b20 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -252,6 +252,7 @@ static inline void mminit_validate_memmodel_limits(unsigned long *start_pfn, #define GUP_FLAGS_WRITE 0x01 #define GUP_FLAGS_FORCE 0x02 +#define GUP_FLAGS_DUMP 0x04 int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm, unsigned long start, int len, int flags, diff --git a/mm/memory.c b/mm/memory.c index a8430ff13837..532a55bce6a4 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1174,41 +1174,22 @@ no_page: pte_unmap_unlock(ptep, ptl); if (!pte_none(pte)) return page; - /* Fall through to ZERO_PAGE handling */ + no_page_table: /* * When core dumping an enormous anonymous area that nobody - * has touched so far, we don't want to allocate page tables. + * has touched so far, we don't want to allocate unnecessary pages or + * page tables. Return error instead of NULL to skip handle_mm_fault, + * then get_dump_page() will return NULL to leave a hole in the dump. + * But we can only make this optimization where a hole would surely + * be zero-filled if handle_mm_fault() actually did handle it. */ - if (flags & FOLL_ANON) { - page = ZERO_PAGE(0); - if (flags & FOLL_GET) - get_page(page); - BUG_ON(flags & FOLL_WRITE); - } + if ((flags & FOLL_DUMP) && + (!vma->vm_ops || !vma->vm_ops->fault)) + return ERR_PTR(-EFAULT); return page; } -/* Can we do the FOLL_ANON optimization? */ -static inline int use_zero_page(struct vm_area_struct *vma) -{ - /* - * We don't want to optimize FOLL_ANON for make_pages_present() - * when it tries to page in a VM_LOCKED region. As to VM_SHARED, - * we want to get the page from the page tables to make sure - * that we serialize and update with any other user of that - * mapping. - */ - if (vma->vm_flags & (VM_LOCKED | VM_SHARED)) - return 0; - /* - * And if we have a fault routine, it's not an anonymous region. - */ - return !vma->vm_ops || !vma->vm_ops->fault; -} - - - int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm, unsigned long start, int nr_pages, int flags, struct page **pages, struct vm_area_struct **vmas) @@ -1288,8 +1269,8 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm, foll_flags = FOLL_TOUCH; if (pages) foll_flags |= FOLL_GET; - if (!write && use_zero_page(vma)) - foll_flags |= FOLL_ANON; + if (flags & GUP_FLAGS_DUMP) + foll_flags |= FOLL_DUMP; do { struct page *page; @@ -1446,7 +1427,7 @@ struct page *get_dump_page(unsigned long addr) struct page *page; if (__get_user_pages(current, current->mm, addr, 1, - GUP_FLAGS_FORCE, &page, &vma) < 1) + GUP_FLAGS_FORCE | GUP_FLAGS_DUMP, &page, &vma) < 1) return NULL; if (page == ZERO_PAGE(0)) { page_cache_release(page);