Re: [RFC PATCH 2/2] mm: Batch page_check_references in shrink_page_list sharing the same i_mmap_mutex

[Tim Chen <tim.c.chen@linux.intel.com>]

On Tue, 2012-08-21 at 17:48 -0700, Tim Chen wrote:

> 
> Thanks to Matthew's suggestions on improving the patch. Here's the
> updated version.  It seems to be sane when I booted my machine up.  I
> will put it through more testing when I get a chance.
> 
> Tim
> 

Matthew,

The new patch seems to be causing some of the workloads with mmaped file
read to seg fault.  Will need to dig further to find out why.

Tim


> ---
> Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
> ---
> diff --git a/include/linux/rmap.h b/include/linux/rmap.h
> index fd07c45..f1320b1 100644
> --- a/include/linux/rmap.h
> +++ b/include/linux/rmap.h
> @@ -156,8 +156,11 @@ static inline void page_dup_rmap(struct page *page)
>  /*
>   * Called from mm/vmscan.c to handle paging out
>   */
> -int page_referenced(struct page *, int is_locked,
> -			struct mem_cgroup *memcg, unsigned long *vm_flags);
> +int needs_page_mmap_mutex(struct page *page);
> +int page_referenced(struct page *, int is_locked, struct mem_cgroup *memcg,
> +				unsigned long *vm_flags);
> +int __page_referenced(struct page *, int is_locked, struct mem_cgroup *memcg,
> +				unsigned long *vm_flags);
>  int page_referenced_one(struct page *, struct vm_area_struct *,
>  	unsigned long address, unsigned int *mapcount, unsigned long *vm_flags);
>  
> @@ -176,6 +179,7 @@ enum ttu_flags {
>  bool is_vma_temporary_stack(struct vm_area_struct *vma);
>  
>  int try_to_unmap(struct page *, enum ttu_flags flags);
> +int __try_to_unmap(struct page *, enum ttu_flags flags);
>  int try_to_unmap_one(struct page *, struct vm_area_struct *,
>  			unsigned long address, enum ttu_flags flags);
>  
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 5b5ad58..ca8cd21 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -843,8 +843,7 @@ static int page_referenced_file(struct page *page,
>  	 * so we can safely take mapping->i_mmap_mutex.
>  	 */
>  	BUG_ON(!PageLocked(page));
> -
> -	mutex_lock(&mapping->i_mmap_mutex);
> +	BUG_ON(!mutex_is_locked(&mapping->i_mmap_mutex));
>  
>  	/*
>  	 * i_mmap_mutex does not stabilize mapcount at all, but mapcount
> @@ -869,21 +868,16 @@ static int page_referenced_file(struct page *page,
>  			break;
>  	}
>  
> -	mutex_unlock(&mapping->i_mmap_mutex);
>  	return referenced;
>  }
>  
> -/**
> - * page_referenced - test if the page was referenced
> - * @page: the page to test
> - * @is_locked: caller holds lock on the page
> - * @memcg: target memory cgroup
> - * @vm_flags: collect encountered vma->vm_flags who actually referenced the page
> - *
> - * Quick test_and_clear_referenced for all mappings to a page,
> - * returns the number of ptes which referenced the page.
> - */
> -int page_referenced(struct page *page,
> +int needs_page_mmap_mutex(struct page *page)
> +{
> +	return page->mapping && page_mapped(page) && page_rmapping(page) &&
> +		!PageKsm(page) && !PageAnon(page);
> +}
> +
> +int __page_referenced(struct page *page,
>  		    int is_locked,
>  		    struct mem_cgroup *memcg,
>  		    unsigned long *vm_flags)
> @@ -919,6 +913,32 @@ out:
>  	return referenced;
>  }
>  
> +/**
> + * page_referenced - test if the page was referenced
> + * @page: the page to test
> + * @is_locked: caller holds lock on the page
> + * @memcg: target memory cgroup
> + * @vm_flags: collect encountered vma->vm_flags who actually referenced the page
> + *
> + * Quick test_and_clear_referenced for all mappings to a page,
> + * returns the number of ptes which referenced the page.
> + */
> +int page_referenced(struct page *page,
> +		    int is_locked,
> +		    struct mem_cgroup *memcg,
> +		    unsigned long *vm_flags)
> +{
> +	int result, needs_lock;
> +
> +	needs_lock = needs_page_mmap_mutex(page);
> +	if (needs_lock)
> +		mutex_lock(&page->mapping->i_mmap_mutex);
> +	result = __page_referenced(page, is_locked, memcg, vm_flags);
> +	if (needs_lock)
> +		mutex_unlock(&page->mapping->i_mmap_mutex);
> +	return result;
> +}
> +
>  static int page_mkclean_one(struct page *page, struct vm_area_struct *vma,
>  			    unsigned long address)
>  {
> @@ -1560,7 +1580,7 @@ static int try_to_unmap_file(struct page *page, enum ttu_flags flags)
>  	unsigned long max_nl_size = 0;
>  	unsigned int mapcount;
>  
> -	mutex_lock(&mapping->i_mmap_mutex);
> +	BUG_ON(!mutex_is_locked(&mapping->i_mmap_mutex));
>  	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
>  		unsigned long address = vma_address(page, vma);
>  		if (address == -EFAULT)
> @@ -1640,7 +1660,24 @@ static int try_to_unmap_file(struct page *page, enum ttu_flags flags)
>  	list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.vm_set.list)
>  		vma->vm_private_data = NULL;
>  out:
> -	mutex_unlock(&mapping->i_mmap_mutex);
> +	return ret;
> +}
> +
> +int __try_to_unmap(struct page *page, enum ttu_flags flags)
> +{
> +	int ret;
> +
> +	BUG_ON(!PageLocked(page));
> +	VM_BUG_ON(!PageHuge(page) && PageTransHuge(page));
> +
> +	if (unlikely(PageKsm(page)))
> +		ret = try_to_unmap_ksm(page, flags);
> +	else if (PageAnon(page))
> +		ret = try_to_unmap_anon(page, flags);
> +	else
> +		ret = try_to_unmap_file(page, flags);
> +	if (ret != SWAP_MLOCK && !page_mapped(page))
> +		ret = SWAP_SUCCESS;
>  	return ret;
>  }
>  
> @@ -1660,20 +1697,27 @@ out:
>   */
>  int try_to_unmap(struct page *page, enum ttu_flags flags)
>  {
> -	int ret;
> +	int result, needs_lock;
> +
> +	needs_lock = needs_page_mmap_mutex(page);
> +	if (needs_lock)
> +		mutex_lock(&page->mapping->i_mmap_mutex);
> +	result = __try_to_unmap(page, flags);
> +	if (needs_lock)
> +		mutex_unlock(&page->mapping->i_mmap_mutex);
> +	return result;
> +}
>  
> -	BUG_ON(!PageLocked(page));
> -	VM_BUG_ON(!PageHuge(page) && PageTransHuge(page));
> +int __try_to_munlock(struct page *page)
> +{
> +	VM_BUG_ON(!PageLocked(page) || PageLRU(page));
>  
>  	if (unlikely(PageKsm(page)))
> -		ret = try_to_unmap_ksm(page, flags);
> +		return try_to_unmap_ksm(page, TTU_MUNLOCK);
>  	else if (PageAnon(page))
> -		ret = try_to_unmap_anon(page, flags);
> +		return try_to_unmap_anon(page, TTU_MUNLOCK);
>  	else
> -		ret = try_to_unmap_file(page, flags);
> -	if (ret != SWAP_MLOCK && !page_mapped(page))
> -		ret = SWAP_SUCCESS;
> -	return ret;
> +		return try_to_unmap_file(page, TTU_MUNLOCK);
>  }
>  
>  /**
> @@ -1693,14 +1737,15 @@ int try_to_unmap(struct page *page, enum ttu_flags flags)
>   */
>  int try_to_munlock(struct page *page)
>  {
> -	VM_BUG_ON(!PageLocked(page) || PageLRU(page));
> -
> -	if (unlikely(PageKsm(page)))
> -		return try_to_unmap_ksm(page, TTU_MUNLOCK);
> -	else if (PageAnon(page))
> -		return try_to_unmap_anon(page, TTU_MUNLOCK);
> -	else
> -		return try_to_unmap_file(page, TTU_MUNLOCK);
> +	int result, needs_lock;
> +
> +	needs_lock = needs_page_mmap_mutex(page);
> +	if (needs_lock)
> +		mutex_lock(&page->mapping->i_mmap_mutex);
> +	result = __try_to_munlock(page);
> +	if (needs_lock)
> +		mutex_unlock(&page->mapping->i_mmap_mutex);
> +	return result;
>  }
>  
>  void __put_anon_vma(struct anon_vma *anon_vma)
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index d4ab646..74a5fd0 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -27,6 +27,7 @@
>  					buffer_heads_over_limit */
>  #include <linux/mm_inline.h>
>  #include <linux/backing-dev.h>
> +#include <linux/ksm.h>
>  #include <linux/rmap.h>
>  #include <linux/topology.h>
>  #include <linux/cpu.h>
> @@ -786,7 +787,7 @@ static enum page_references page_check_references(struct page *page,
>  	int referenced_ptes, referenced_page;
>  	unsigned long vm_flags;
>  
> -	referenced_ptes = page_referenced(page, 1, mz->mem_cgroup, &vm_flags);
> +	referenced_ptes = __page_referenced(page, 1, mz->mem_cgroup, &vm_flags);
>  	referenced_page = TestClearPageReferenced(page);
>  
>  	/* Lumpy reclaim - ignore references */
> @@ -856,6 +857,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
>  	unsigned long nr_congested = 0;
>  	unsigned long nr_reclaimed = 0;
>  	unsigned long nr_writeback = 0;
> +	struct mutex *i_mmap_mutex = NULL;
>  
>  	cond_resched();
>  
> @@ -909,7 +911,15 @@ static unsigned long shrink_page_list(struct list_head *page_list,
>  			}
>  		}
>  
> +		if (needs_page_mmap_mutex(page) &&
> +			       i_mmap_mutex != &page->mapping->i_mmap_mutex) {
> +			if (i_mmap_mutex)
> +				mutex_unlock(i_mmap_mutex);
> +			i_mmap_mutex = &page->mapping->i_mmap_mutex;
> +			mutex_lock(i_mmap_mutex);
> +		}
>  		references = page_check_references(page, mz, sc);
> +
>  		switch (references) {
>  		case PAGEREF_ACTIVATE:
>  			goto activate_locked;
> @@ -939,7 +949,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
>  		 * processes. Try to unmap it here.
>  		 */
>  		if (page_mapped(page) && mapping) {
> -			switch (try_to_unmap(page, TTU_UNMAP)) {
> +			switch (__try_to_unmap(page, TTU_UNMAP)) {
>  			case SWAP_FAIL:
>  				goto activate_locked;
>  			case SWAP_AGAIN:
> @@ -1090,6 +1100,8 @@ keep_lumpy:
>  		VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
>  	}
>  
> +	if (i_mmap_mutex)
> +		mutex_unlock(i_mmap_mutex);
>  	nr_reclaimed += __remove_mapping_batch(&unmap_pages, &ret_pages,
>  					       &free_pages);
>  
> 
> 
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