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SubjectRe: [Patch] tmpfs: clean up shmem_find_get_pages_and_swap()
On Tue, 24 Jan 2012, Cong Wang wrote:

> This patch cleans up shmem_find_get_pages_and_swap() interface:
>
> a) Pass struct pagevec* instead of ->pages
> b) Check if nr_pages is greater than PAGEVEC_SIZE inside the function
> c) Return the result via ->nr instead of using return value
>
> Compiling test only.
>
> Cc: Hugh Dickins <hughd@google.com>
> Signed-off-by: WANG Cong <xiyou.wangcong@gmail.com>

I don't see any cleanup: just a difference in taste, I suppose.

shmem_find_get_pages_and_swap() is modelled on find_get_pages():
I'd prefer to keep it that way unless there's good reason to diverge.

I do see a slight change in behaviour, where you've undone the range
limitation (coming from invalidate_inode_pages2_range() originally, but
now in several functions in mm/truncate.c). I think you misunderstood

> - min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1,

When doing a range, that's trying to stop the radix_tree gang lookup
looking further than could ever be necessary. Not a big deal, it is
imperfect anyway - makes more sense when the range is 1 than larger;
but shouldn't be undone without justification.

Hugh

>
> ---
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 269d049..c4e08e2 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -312,15 +312,19 @@ static void shmem_delete_from_page_cache(struct page *page, void *radswap)
> /*
> * Like find_get_pages, but collecting swap entries as well as pages.
> */
> -static unsigned shmem_find_get_pages_and_swap(struct address_space *mapping,
> +static void shmem_find_get_pages_and_swap(struct address_space *mapping,
> pgoff_t start, unsigned int nr_pages,
> - struct page **pages, pgoff_t *indices)
> + struct pagevec *pvec, pgoff_t *indices)
> {
> unsigned int i;
> unsigned int ret;
> unsigned int nr_found;
> + struct page **pages = pvec->pages;
>
> rcu_read_lock();
> +
> + if (nr_pages > PAGEVEC_SIZE)
> + nr_pages = PAGEVEC_SIZE;
> restart:
> nr_found = radix_tree_gang_lookup_slot(&mapping->page_tree,
> (void ***)pages, indices, start, nr_pages);
> @@ -357,7 +361,7 @@ export:
> if (unlikely(!ret && nr_found))
> goto restart;
> rcu_read_unlock();
> - return ret;
> + pvec->nr = ret;
> }
>
> /*
> @@ -409,8 +413,8 @@ void shmem_unlock_mapping(struct address_space *mapping)
> * Avoid pagevec_lookup(): find_get_pages() returns 0 as if it
> * has finished, if it hits a row of PAGEVEC_SIZE swap entries.
> */
> - pvec.nr = shmem_find_get_pages_and_swap(mapping, index,
> - PAGEVEC_SIZE, pvec.pages, indices);
> + shmem_find_get_pages_and_swap(mapping, index,
> + PAGEVEC_SIZE, &pvec, indices);
> if (!pvec.nr)
> break;
> index = indices[pvec.nr - 1] + 1;
> @@ -442,9 +446,8 @@ void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
> pagevec_init(&pvec, 0);
> index = start;
> while (index <= end) {
> - pvec.nr = shmem_find_get_pages_and_swap(mapping, index,
> - min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1,
> - pvec.pages, indices);
> + shmem_find_get_pages_and_swap(mapping, index,
> + end - index + 1, &pvec, indices);
> if (!pvec.nr)
> break;
> mem_cgroup_uncharge_start();
> @@ -490,9 +493,8 @@ void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
> index = start;
> for ( ; ; ) {
> cond_resched();
> - pvec.nr = shmem_find_get_pages_and_swap(mapping, index,
> - min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1,
> - pvec.pages, indices);
> + shmem_find_get_pages_and_swap(mapping, index,
> + end - index + 1, &pvec, indices);
> if (!pvec.nr) {
> if (index == start)
> break;


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