Re: [PATCH 4/4] MADV_VOLATILE: Add page purging logic & SIGBUS trap

[Minchan Kim <minchan@kernel.org>]

On Tue, Apr 29, 2014 at 02:21:23PM -0700, John Stultz wrote:
> This patch adds the hooks in the vmscan logic to purge volatile pages
> and mark their pte as purged. With this, volatile pages will be purged
> under pressure, and their ptes swap entry's marked. If the purged pages
> are accessed before being marked non-volatile, we catch this and send a
> SIGBUS.
> 
> This is a simplified implementation that uses logic from Minchan's earlier
> efforts, so credit to Minchan for his work.
> 
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Android Kernel Team <kernel-team@android.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Robert Love <rlove@google.com>
> Cc: Mel Gorman <mel@csn.ul.ie>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Dave Hansen <dave@sr71.net>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: Dmitry Adamushko <dmitry.adamushko@gmail.com>
> Cc: Neil Brown <neilb@suse.de>
> Cc: Andrea Arcangeli <aarcange@redhat.com>
> Cc: Mike Hommey <mh@glandium.org>
> Cc: Taras Glek <tglek@mozilla.com>
> Cc: Jan Kara <jack@suse.cz>
> Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
> Cc: Michel Lespinasse <walken@google.com>
> Cc: Minchan Kim <minchan@kernel.org>
> Cc: Keith Packard <keithp@keithp.com>
> Cc: linux-mm@kvack.org <linux-mm@kvack.org>
> Signed-off-by: John Stultz <john.stultz@linaro.org>
> ---
>  include/linux/mvolatile.h |   1 +
>  mm/internal.h             |   2 -
>  mm/memory.c               |   7 +++
>  mm/mvolatile.c            | 119 ++++++++++++++++++++++++++++++++++++++++++++++
>  mm/rmap.c                 |   5 ++
>  mm/vmscan.c               |  12 +++++
>  6 files changed, 144 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/mvolatile.h b/include/linux/mvolatile.h
> index f53396b..8b797b7 100644
> --- a/include/linux/mvolatile.h
> +++ b/include/linux/mvolatile.h
> @@ -2,5 +2,6 @@
>  #define _LINUX_MVOLATILE_H
>  
>  int madvise_volatile(int bhv, unsigned long start, unsigned long end);
> +extern int purge_volatile_page(struct page *page);
>  
>  #endif /* _LINUX_MVOLATILE_H */
> diff --git a/mm/internal.h b/mm/internal.h
> index 07b6736..2213055 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -240,10 +240,8 @@ static inline void mlock_migrate_page(struct page *newpage, struct page *page)
>  
>  extern pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma);
>  
> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>  extern unsigned long vma_address(struct page *page,
>  				 struct vm_area_struct *vma);
> -#endif
>  #else /* !CONFIG_MMU */
>  static inline int mlocked_vma_newpage(struct vm_area_struct *v, struct page *p)
>  {
> diff --git a/mm/memory.c b/mm/memory.c
> index 037b812..cf024bd 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -61,6 +61,7 @@
>  #include <linux/string.h>
>  #include <linux/dma-debug.h>
>  #include <linux/debugfs.h>
> +#include <linux/mvolatile.h>
>  
>  #include <asm/io.h>
>  #include <asm/pgalloc.h>
> @@ -3067,6 +3068,12 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
>  			migration_entry_wait(mm, pmd, address);
>  		} else if (is_hwpoison_entry(entry)) {
>  			ret = VM_FAULT_HWPOISON;
> +		} else if (is_purged_entry(entry)) {
> +			page_table = pte_offset_map_lock(mm, pmd, address,
> +									&ptl);
> +			if (likely(pte_same(*page_table, orig_pte)))
> +				ret = VM_FAULT_SIGBUS;
> +			goto unlock;
>  		} else {
>  			print_bad_pte(vma, address, orig_pte, NULL);
>  			ret = VM_FAULT_SIGBUS;
> diff --git a/mm/mvolatile.c b/mm/mvolatile.c
> index 555d5c4..a7831d3 100644
> --- a/mm/mvolatile.c
> +++ b/mm/mvolatile.c
> @@ -232,3 +232,122 @@ out:
>  
>  	return ret;
>  }
> +
> +
> +/**
> + * try_to_purge_one - Purge a volatile page from a vma
> + * @page: page to purge
> + * @vma: vma to purge page from
> + *
> + * Finds the pte for a page in a vma, marks the pte as purged
> + * and release the page.
> + */
> +static void try_to_purge_one(struct page *page, struct vm_area_struct *vma)
> +{
> +	struct mm_struct *mm = vma->vm_mm;
> +	pte_t *pte;
> +	pte_t pteval;
> +	spinlock_t *ptl;
> +	unsigned long addr;
> +
> +	VM_BUG_ON(!PageLocked(page));
> +
> +	addr = vma_address(page, vma);
> +	pte = page_check_address(page, mm, addr, &ptl, 0);
> +	if (!pte)
> +		return;
> +
> +	BUG_ON(vma->vm_flags & (VM_SPECIAL|VM_LOCKED|VM_MIXEDMAP|VM_HUGETLB));
> +
> +	flush_cache_page(vma, addr, page_to_pfn(page));
> +	pteval = ptep_clear_flush(vma, addr, pte);
> +
> +	update_hiwater_rss(mm);
> +	if (PageAnon(page))
> +		dec_mm_counter(mm, MM_ANONPAGES);
> +	else
> +		dec_mm_counter(mm, MM_FILEPAGES);

We can add file-backed page part later when we move to suppport vrange-file.

> +
> +	page_remove_rmap(page);
> +	page_cache_release(page);
> +
> +	set_pte_at(mm, addr, pte, swp_entry_to_pte(make_purged_entry()));
> +
> +	pte_unmap_unlock(pte, ptl);
> +	mmu_notifier_invalidate_page(mm, addr);
> +}
> +
> +
> +/**
> + * try_to_purge_vpage - check vma chain and purge from vmas marked volatile
> + * @page: page to purge
> + *
> + * Goes over all the vmas that hold a page, and where the vmas are volatile,
> + * purge the page from the vma.
> + *
> + * Returns 0 on success, -1 on error.
> + */
> +static int try_to_purge_vpage(struct page *page)
> +{
> +	struct anon_vma *anon_vma;
> +	struct anon_vma_chain *avc;
> +	pgoff_t pgoff;
> +	int ret = 0;
> +
> +	anon_vma = page_lock_anon_vma_read(page);
> +	if (!anon_vma)
> +		return -1;
> +
> +	pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
> +	/*
> +	 * During interating the loop, some processes could see a page as
> +	 * purged while others could see a page as not-purged because we have
> +	 * no global lock between parent and child for protecting mvolatile
> +	 * system call during this loop. But it's not a problem because the
> +	 * page is  not *SHARED* page but *COW* page so parent and child can
> +	 * see other data anytime. The worst case by this race is a page was
> +	 * purged but couldn't be discarded so it makes unnecessary pagefault
> +	 * but it wouldn't be severe.
> +	 */
> +	anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
> +		struct vm_area_struct *vma = avc->vma;
> +
> +		if (!(vma->vm_flags & VM_VOLATILE)) {
> +			ret = -1;
> +			break;
> +		}
> +		try_to_purge_one(page, vma);
> +	}
> +	page_unlock_anon_vma_read(anon_vma);
> +	return ret;
> +}
> +
> +
> +/**
> + * purge_volatile_page - If possible, purge the specified volatile page
> + * @page: page to purge
> + *
> + * Attempts to purge a volatile page, and if needed frees the swap page
> + *
> + * Returns 0 on success, -1 on error.
> + */
> +int purge_volatile_page(struct page *page)
> +{
> +	VM_BUG_ON(!PageLocked(page));
> +	VM_BUG_ON(PageLRU(page));
> +
> +	/* XXX - for now we only support anonymous volatile pages */
> +	if (!PageAnon(page))
> +		return -1;
> +
> +	if (!try_to_purge_vpage(page)) {
> +		if (PageSwapCache(page))
> +			try_to_free_swap(page);
> +
> +		if (page_freeze_refs(page, 1)) {
> +			unlock_page(page);
> +			return 0;
> +		}
> +	}
> +	return -1;
> +}
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 9c3e773..efb5c61 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -728,6 +728,11 @@ int page_referenced_one(struct page *page, struct vm_area_struct *vma,
>  				referenced++;
>  		}
>  		pte_unmap_unlock(pte, ptl);
> +		if (vma->vm_flags & VM_VOLATILE) {
> +			pra->mapcount = 0;
> +			pra->vm_flags |= VM_VOLATILE;
> +			return SWAP_FAIL;
> +		}
>  	}
>  
>  	if (referenced) {
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 3f56c8d..a267926 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -43,6 +43,7 @@
>  #include <linux/sysctl.h>
>  #include <linux/oom.h>
>  #include <linux/prefetch.h>
> +#include <linux/mvolatile.h>
>  
>  #include <asm/tlbflush.h>
>  #include <asm/div64.h>
> @@ -697,6 +698,7 @@ enum page_references {
>  	PAGEREF_RECLAIM,
>  	PAGEREF_RECLAIM_CLEAN,
>  	PAGEREF_KEEP,
> +	PAGEREF_PURGE,
>  	PAGEREF_ACTIVATE,
>  };
>  
> @@ -717,6 +719,13 @@ static enum page_references page_check_references(struct page *page,
>  	if (vm_flags & VM_LOCKED)
>  		return PAGEREF_RECLAIM;
>  
> +	/*
> +	 * If volatile page is reached on LRU's tail, we discard the
> +	 * page without considering recycle the page.
> +	 */
> +	if (vm_flags & VM_VOLATILE)
> +		return PAGEREF_PURGE;
> +
>  	if (referenced_ptes) {
>  		if (PageSwapBacked(page))
>  			return PAGEREF_ACTIVATE;
> @@ -944,6 +953,9 @@ static unsigned long shrink_page_list(struct list_head *page_list,
>  		switch (references) {
>  		case PAGEREF_ACTIVATE:
>  			goto activate_locked;
> +		case PAGEREF_PURGE:
> +			if (!purge_volatile_page(page))
> +				goto free_it;
>  		case PAGEREF_KEEP:
>  			goto keep_locked;
>  		case PAGEREF_RECLAIM:
> -- 
> 1.9.1
> 
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-- 
Kind regards,
Minchan Kim