Re: [PATCH] filemap: optimize order0 folio in filemap_map_pages

[Matthew Wilcox <willy@infradead.org>]

On Tue, Aug 19, 2025 at 10:06:53PM +0800, Jinjiang Tu wrote:
> There are two meaningless folio refcount update for order0 folio in
> filemap_map_pages(). First, filemap_map_order0_folio() adds folio refcount
> after the folio is mapped to pte. And then, filemap_map_pages() drops a
> refcount grabbed by next_uptodate_folio(). We could remain the refcount
> unchanged in this case.
> 
> With this patch, we can get 8% performance gain for lmbench testcase
> 'lat_pagefault -P 1 file', the size of file is 512M.

You don't explain why you move the folio_unlock() call

> Signed-off-by: Jinjiang Tu <tujinjiang@huawei.com>
> ---
>  mm/filemap.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 751838ef05e5..5de52deab138 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -3693,6 +3693,8 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
>  	}
>  
>  	vmf->pte = old_ptep;
> +	folio_unlock(folio);
> +	folio_put(folio);
>  
>  	return ret;
>  }
> @@ -3705,7 +3707,7 @@ static vm_fault_t filemap_map_order0_folio(struct vm_fault *vmf,
>  	struct page *page = &folio->page;
>  
>  	if (PageHWPoison(page))
> -		return ret;
> +		goto out;
>  
>  	/* See comment of filemap_map_folio_range() */
>  	if (!folio_test_workingset(folio))
> @@ -3717,15 +3719,19 @@ static vm_fault_t filemap_map_order0_folio(struct vm_fault *vmf,
>  	 * the fault-around logic.
>  	 */
>  	if (!pte_none(ptep_get(vmf->pte)))
> -		return ret;
> +		goto out;
>  
>  	if (vmf->address == addr)
>  		ret = VM_FAULT_NOPAGE;
>  
>  	set_pte_range(vmf, folio, page, 1, addr);
>  	(*rss)++;
> -	folio_ref_inc(folio);
> +	folio_unlock(folio);
> +	return ret;
>  
> +out:
> +	folio_unlock(folio);
> +	folio_put(folio);
>  	return ret;
>  }
>  
> @@ -3783,9 +3789,6 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
>  			ret |= filemap_map_folio_range(vmf, folio,
>  					xas.xa_index - folio->index, addr,
>  					nr_pages, &rss, &mmap_miss);
> -
> -		folio_unlock(folio);
> -		folio_put(folio);
>  	} while ((folio = next_uptodate_folio(&xas, mapping, end_pgoff)) != NULL);
>  	add_mm_counter(vma->vm_mm, folio_type, rss);
>  	pte_unmap_unlock(vmf->pte, vmf->ptl);
> -- 
> 2.43.0
> 
>