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Date: Mon, 21 Sep 2009 19:02:29 +0100 (BST)
From: Hugh Dickins <hugh.dickins@...cali.co.uk>
To: Johannes Weiner <hannes@...xchg.org>
cc: KOSAKI Motohiro <kosaki.motohiro@...il.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Mel Gorman <mel@....ul.ie>,
Christoph Lameter <cl@...ux-foundation.org>,
LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
Hugh Dickins <hugh.dickins@...cali.co.uk>,
Lee Schermerhorn <Lee.Schermerhorn@...com>
Subject: Re: a patch drop request in -mm
On Mon, 21 Sep 2009, Johannes Weiner wrote:
>
> This calls unmap_mapping_range() before actually munlocking the page.
>
> Other unmappers like do_munmap() and exit_mmap() munlock explicitely
> before unmapping.
>
> We could do the same here but I would argue that mlock lifetime
> depends on actual userspace mappings and then move the munlocking a
> few levels down into the unmapping guts to make this implicit.
>
> Because truncation makes sure pages get unmapped, this is handled too.
>
> Below is roughly outlined and untested demonstration patch. What do
> you think?
That certainly looks appealing, but is it actually correct?
I'm thinking that munlock_vma_pages_range() clears VM_LOCKED
from vm_flags, which would be incorrect in the truncation case;
and that the VM_NONLINEAR truncation case only zaps certain
pages in the larger range that it is applied to.
Hugh
> diff --git a/mm/internal.h b/mm/internal.h
> index f290c4d..0d3c6c6 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -67,10 +67,6 @@ extern long mlock_vma_pages_range(struct vm_area_struct *vma,
> unsigned long start, unsigned long end);
> extern void munlock_vma_pages_range(struct vm_area_struct *vma,
> unsigned long start, unsigned long end);
> -static inline void munlock_vma_pages_all(struct vm_area_struct *vma)
> -{
> - munlock_vma_pages_range(vma, vma->vm_start, vma->vm_end);
> -}
> #endif
>
> /*
> diff --git a/mm/memory.c b/mm/memory.c
> index aede2ce..f8c5ac6 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -971,7 +971,7 @@ unsigned long unmap_vmas(struct mmu_gather **tlbp,
>
> mmu_notifier_invalidate_range_start(mm, start_addr, end_addr);
> for ( ; vma && vma->vm_start < end_addr; vma = vma->vm_next) {
> - unsigned long end;
> + unsigned long end, nr_pages;
>
> start = max(vma->vm_start, start_addr);
> if (start >= vma->vm_end)
> @@ -980,8 +980,15 @@ unsigned long unmap_vmas(struct mmu_gather **tlbp,
> if (end <= vma->vm_start)
> continue;
>
> + nr_pages = (end - start) >> PAGE_SHIFT;
> +
> + if (vma->vm_flags & VM_LOCKED) {
> + mm->locked_vm -= nr_pages;
> + munlock_vma_pages_range(vma, start, end);
> + }
> +
> if (vma->vm_flags & VM_ACCOUNT)
> - *nr_accounted += (end - start) >> PAGE_SHIFT;
> + *nr_accounted += nr_pages;
>
> if (unlikely(is_pfn_mapping(vma)))
> untrack_pfn_vma(vma, 0, 0);
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 8101de4..02189f3 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1921,20 +1921,6 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len)
> vma = prev? prev->vm_next: mm->mmap;
>
> /*
> - * unlock any mlock()ed ranges before detaching vmas
> - */
> - if (mm->locked_vm) {
> - struct vm_area_struct *tmp = vma;
> - while (tmp && tmp->vm_start < end) {
> - if (tmp->vm_flags & VM_LOCKED) {
> - mm->locked_vm -= vma_pages(tmp);
> - munlock_vma_pages_all(tmp);
> - }
> - tmp = tmp->vm_next;
> - }
> - }
> -
> - /*
> * Remove the vma's, and unmap the actual pages
> */
> detach_vmas_to_be_unmapped(mm, vma, prev, end);
> @@ -2089,15 +2075,6 @@ void exit_mmap(struct mm_struct *mm)
> /* mm's last user has gone, and its about to be pulled down */
> mmu_notifier_release(mm);
>
> - if (mm->locked_vm) {
> - vma = mm->mmap;
> - while (vma) {
> - if (vma->vm_flags & VM_LOCKED)
> - munlock_vma_pages_all(vma);
> - vma = vma->vm_next;
> - }
> - }
> -
> arch_exit_mmap(mm);
>
> vma = mm->mmap;
> diff --git a/mm/truncate.c b/mm/truncate.c
> index ccc3ecf..a4e3b8f 100644
> --- a/mm/truncate.c
> +++ b/mm/truncate.c
> @@ -104,7 +104,6 @@ truncate_complete_page(struct address_space *mapping, struct page *page)
>
> cancel_dirty_page(page, PAGE_CACHE_SIZE);
>
> - clear_page_mlock(page);
> remove_from_page_cache(page);
> ClearPageMappedToDisk(page);
> page_cache_release(page); /* pagecache ref */
> @@ -129,7 +128,6 @@ invalidate_complete_page(struct address_space *mapping, struct page *page)
> if (page_has_private(page) && !try_to_release_page(page, 0))
> return 0;
>
> - clear_page_mlock(page);
> ret = remove_mapping(mapping, page);
>
> return ret;
> @@ -348,7 +346,6 @@ invalidate_complete_page2(struct address_space *mapping, struct page *page)
> if (PageDirty(page))
> goto failed;
>
> - clear_page_mlock(page);
> BUG_ON(page_has_private(page));
> __remove_from_page_cache(page);
> spin_unlock_irq(&mapping->tree_lock);
>
--
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