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Date: Mon, 18 Nov 2013 13:51:54 -0500
From: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To: Dave Hansen <dave@...1.net>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
dave.jiang@...el.com, akpm@...ux-foundation.org, dhillf@...il.com,
Mel Gorman <mgorman@...e.de>
Subject: Re: [v3][PATCH 2/2] mm: thp: give transparent hugepage code aseparate
copy_page
On Fri, Nov 15, 2013 at 02:55:53PM -0800, Dave Hansen wrote:
>
> Changes from v2:
> *
> Changes from v1:
> * removed explicit might_sleep() in favor of the one that we
> get from the cond_resched();
>
> --
>
> From: Dave Hansen <dave.hansen@...ux.intel.com>
>
> Right now, the migration code in migrate_page_copy() uses
> copy_huge_page() for hugetlbfs and thp pages:
>
> if (PageHuge(page) || PageTransHuge(page))
> copy_huge_page(newpage, page);
>
> So, yay for code reuse. But:
>
> void copy_huge_page(struct page *dst, struct page *src)
> {
> struct hstate *h = page_hstate(src);
>
> and a non-hugetlbfs page has no page_hstate(). This works 99% of
> the time because page_hstate() determines the hstate from the
> page order alone. Since the page order of a THP page matches the
> default hugetlbfs page order, it works.
>
> But, if you change the default huge page size on the boot
> command-line (say default_hugepagesz=1G), then we might not even
> *have* a 2MB hstate so page_hstate() returns null and
> copy_huge_page() oopses pretty fast since copy_huge_page()
> dereferences the hstate:
>
> void copy_huge_page(struct page *dst, struct page *src)
> {
> struct hstate *h = page_hstate(src);
> if (unlikely(pages_per_huge_page(h) > MAX_ORDER_NR_PAGES)) {
> ...
>
> Mel noticed that the migration code is really the only user of
> these functions. This moves all the copy code over to migrate.c
> and makes copy_huge_page() work for THP by checking for it
> explicitly.
>
> I believe the bug was introduced in b32967ff101:
> Author: Mel Gorman <mgorman@...e.de>
> Date: Mon Nov 19 12:35:47 2012 +0000
> mm: numa: Add THP migration for the NUMA working set scanning fault case.
>
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Looks good to me with a few comments below. Thanks.
Reviewed-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> ---
>
> linux.git-davehans/include/linux/hugetlb.h | 4 --
> linux.git-davehans/mm/hugetlb.c | 34 --------------------
> linux.git-davehans/mm/migrate.c | 48 +++++++++++++++++++++++++++++
> 3 files changed, 48 insertions(+), 38 deletions(-)
>
> diff -puN mm/migrate.c~copy-huge-separate-from-copy-transhuge mm/migrate.c
> --- linux.git/mm/migrate.c~copy-huge-separate-from-copy-transhuge 2013-11-15 14:44:55.256970259 -0800
> +++ linux.git-davehans/mm/migrate.c 2013-11-15 14:45:17.457963844 -0800
> @@ -442,6 +442,54 @@ int migrate_huge_page_move_mapping(struc
> }
>
> /*
> + * Gigantic pages are so large that the we do not guarantee
s/the // ?
> + * that page++ pointer arithmetic will work across the
> + * entire page. We need something more specialized.
> + */
> +static void __copy_gigantic_page(struct page *dst, struct page *src,
> + int nr_pages)
> +{
> + int i;
> + struct page *dst_base = dst;
> + struct page *src_base = src;
> +
> + for (i = 0; i < nr_pages; ) {
> + cond_resched();
I think that this cond_resched() seems to be called too often.
One cond_resched() per MAX_ORDER_NR_PAGES pages copy looks better
than per single page copy. So I'll post a separate patch for this
which is appled on top of your patches.
> + copy_highpage(dst, src);
> +
> + i++;
> + dst = mem_map_next(dst, dst_base, i);
> + src = mem_map_next(src, src_base, i);
> + }
> +}
> +
> +static void copy_huge_page(struct page *dst, struct page *src)
> +{
> + int i;
> + int nr_pages;
> +
> + if (PageHuge(src)) {
> + /* hugetlbfs page */
> + struct hstate *h = page_hstate(src);
> + nr_pages = pages_per_huge_page(h);
> +
> + if (unlikely(nr_pages > MAX_ORDER_NR_PAGES)) {
> + __copy_gigantic_page(dst, src, nr_pages);
> + return;
> + }
> + } else {
> + /* thp page */
> + BUG_ON(!PageTransHuge(src));
> + nr_pages = hpage_nr_pages(src);
> + }
> +
> + for (i = 0; i < nr_pages; i++ ) {
Coding style violation?
ERROR: space prohibited before that close parenthesis ')'
#177: FILE: mm/migrate.c:486:
+ for (i = 0; i < nr_pages; i++ ) {
Thanks,
Naoya Horiguchi
> + cond_resched();
> + copy_highpage(dst + i, src + i);
> + }
> +}
> +
> +/*
> * Copy the page to its new location
> */
> void migrate_page_copy(struct page *newpage, struct page *page)
> diff -puN mm/hugetlb.c~copy-huge-separate-from-copy-transhuge mm/hugetlb.c
> --- linux.git/mm/hugetlb.c~copy-huge-separate-from-copy-transhuge 2013-11-15 14:44:55.261970484 -0800
> +++ linux.git-davehans/mm/hugetlb.c 2013-11-15 14:44:55.389976227 -0800
> @@ -476,40 +476,6 @@ static int vma_has_reserves(struct vm_ar
> return 0;
> }
>
> -static void copy_gigantic_page(struct page *dst, struct page *src)
> -{
> - int i;
> - struct hstate *h = page_hstate(src);
> - struct page *dst_base = dst;
> - struct page *src_base = src;
> -
> - for (i = 0; i < pages_per_huge_page(h); ) {
> - cond_resched();
> - copy_highpage(dst, src);
> -
> - i++;
> - dst = mem_map_next(dst, dst_base, i);
> - src = mem_map_next(src, src_base, i);
> - }
> -}
> -
> -void copy_huge_page(struct page *dst, struct page *src)
> -{
> - int i;
> - struct hstate *h = page_hstate(src);
> -
> - if (unlikely(pages_per_huge_page(h) > MAX_ORDER_NR_PAGES)) {
> - copy_gigantic_page(dst, src);
> - return;
> - }
> -
> - might_sleep();
> - for (i = 0; i < pages_per_huge_page(h); i++) {
> - cond_resched();
> - copy_highpage(dst + i, src + i);
> - }
> -}
> -
> static void enqueue_huge_page(struct hstate *h, struct page *page)
> {
> int nid = page_to_nid(page);
> diff -puN include/linux/hugetlb.h~copy-huge-separate-from-copy-transhuge include/linux/hugetlb.h
> --- linux.git/include/linux/hugetlb.h~copy-huge-separate-from-copy-transhuge 2013-11-15 14:44:55.263970574 -0800
> +++ linux.git-davehans/include/linux/hugetlb.h 2013-11-15 14:44:55.325973356 -0800
> @@ -69,7 +69,6 @@ int dequeue_hwpoisoned_huge_page(struct
> bool isolate_huge_page(struct page *page, struct list_head *list);
> void putback_active_hugepage(struct page *page);
> bool is_hugepage_active(struct page *page);
> -void copy_huge_page(struct page *dst, struct page *src);
>
> #ifdef CONFIG_ARCH_WANT_HUGE_PMD_SHARE
> pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud);
> @@ -140,9 +139,6 @@ static inline int dequeue_hwpoisoned_hug
> #define isolate_huge_page(p, l) false
> #define putback_active_hugepage(p) do {} while (0)
> #define is_hugepage_active(x) false
> -static inline void copy_huge_page(struct page *dst, struct page *src)
> -{
> -}
>
> static inline unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
> unsigned long address, unsigned long end, pgprot_t newprot)
> _
>
> --
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