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Date: Thu, 27 Feb 2014 13:19:57 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc: Sasha Levin <sasha.levin@...cle.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 2/3] mm, hugetlbfs: fix rmapping for anonymous hugepages
with page_pgoff()
On Wed, 26 Feb 2014 23:39:36 -0500 Naoya Horiguchi <n-horiguchi@...jp.nec.com> wrote:
> page->index stores pagecache index when the page is mapped into file mapping
> region, and the index is in pagecache size unit, so it depends on the page
> size. Some of users of reverse mapping obviously assumes that page->index
> is in PAGE_CACHE_SHIFT unit, so they don't work for anonymous hugepage.
>
> For example, consider that we have 3-hugepage vma and try to mbind the 2nd
> hugepage to migrate to another node. Then the vma is split and migrate_page()
> is called for the 2nd hugepage (belonging to the middle vma.)
> In migrate operation, rmap_walk_anon() tries to find the relevant vma to
> which the target hugepage belongs, but here we miscalculate pgoff.
> So anon_vma_interval_tree_foreach() grabs invalid vma, which fires VM_BUG_ON.
>
> This patch introduces a new API that is usable both for normal page and
> hugepage to get PAGE_SIZE offset from page->index. Users should clearly
> distinguish page_index for pagecache index and page_pgoff for page offset.
So this patch is really independent of the page-walker changes, but the
page walker changes need it. So it is appropriate that this patch be
staged before that series, and separately. Agree?
> Reported-by: Sasha Levin <sasha.levin@...cle.com> # if the reported problem is fixed
> Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> Cc: stable@...r.kernel.org # 3.12+
Why cc:stable? This problem will only cause runtime issues when the
page walker patches are present?
> index 4f591df66778..a8bd14f42032 100644
> --- next-20140220.orig/include/linux/pagemap.h
> +++ next-20140220/include/linux/pagemap.h
> @@ -316,6 +316,19 @@ static inline loff_t page_file_offset(struct page *page)
> return ((loff_t)page_file_index(page)) << PAGE_CACHE_SHIFT;
> }
>
> +extern pgoff_t hugepage_pgoff(struct page *page);
> +
> +/*
> + * page->index stores pagecache index whose unit is not always PAGE_SIZE.
> + * This function converts it into PAGE_SIZE offset.
> + */
> +#define page_pgoff(page) \
> +({ \
> + unlikely(PageHuge(page)) ? \
> + hugepage_pgoff(page) : \
> + page->index >> (PAGE_CACHE_SHIFT - PAGE_SHIFT); \
> +})
- I don't think this needs to be implemented in a macro? Can we do
it in good old C?
- Is PageHuge() the appropriate test?
/*
* PageHuge() only returns true for hugetlbfs pages, but not for normal or
* transparent huge pages. See the PageTransHuge() documentation for more
* details.
*/
- Should page->index be shifted right or left? Probably left - I
doubt if PAGE_CACHE_SHIFT will ever be less than PAGE_SHIFT.
- I'm surprised we don't have a general what-is-this-page's-order
function, so you can just do
static inline pgoff_t page_pgoff(struct page *page)
{
return page->index << page_size_order(page);
}
And I think this would be a better implementation, as the (new)
page_size_order() could be used elsewhere.
page_size_order() would be a crappy name - can't think of anything
better at present.
> --- next-20140220.orig/mm/memory-failure.c
> +++ next-20140220/mm/memory-failure.c
> @@ -404,7 +404,7 @@ static void collect_procs_anon(struct page *page, struct list_head *to_kill,
> if (av == NULL) /* Not actually mapped anymore */
> return;
>
> - pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
See this did a left shift.
> + pgoff = page_pgoff(page);
> read_lock(&tasklist_lock);
> for_each_process (tsk) {
> struct anon_vma_chain *vmac;
> @@ -437,7 +437,7 @@ static void collect_procs_file(struct page *page, struct list_head *to_kill,
> mutex_lock(&mapping->i_mmap_mutex);
> read_lock(&tasklist_lock);
> for_each_process(tsk) {
> - pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
him too.
> + pgoff_t pgoff = page_pgoff(page);
>
> if (!task_early_kill(tsk))
> continue;
> diff --git next-20140220.orig/mm/rmap.c next-20140220/mm/rmap.c
> index 9056a1f00b87..78405051474a 100644
> --- next-20140220.orig/mm/rmap.c
> +++ next-20140220/mm/rmap.c
> @@ -515,11 +515,7 @@ void page_unlock_anon_vma_read(struct anon_vma *anon_vma)
> static inline unsigned long
> __vma_address(struct page *page, struct vm_area_struct *vma)
> {
> - pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
And him.
> -
> - if (unlikely(is_vm_hugetlb_page(vma)))
> - pgoff = page->index << huge_page_order(page_hstate(page));
> -
> + pgoff_t pgoff = page_pgoff(page);
> return vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
> }
>
> @@ -1598,7 +1594,7 @@ static struct anon_vma *rmap_walk_anon_lock(struct page *page,
> static int rmap_walk_anon(struct page *page, struct rmap_walk_control *rwc)
> {
> struct anon_vma *anon_vma;
> - pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
again.
> + pgoff_t pgoff = page_pgoff(page);
> struct anon_vma_chain *avc;
> int ret = SWAP_AGAIN;
--
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