Re: [RFC PATCH v4 3/5] mm/readahead: Make space in struct file_ra_state

Pankaj Raghav (Samsung)
2025-05-09T10:46:58Z

On Wed, Apr 30, 2025 at 03:59:16PM +0100, Ryan Roberts wrote:
> We need to be able to store the preferred folio order associated with a
> readahead request in the struct file_ra_state so that we can more
> accurately increase the order across subsequent readahead requests. But
> struct file_ra_state is per-struct file, so we don't really want to
> increase it's size.
>
> mmap_miss is currently 32 bits but it is only counted up to 10 *
> MMAP_LOTSAMISS, which is currently defined as 1000. So 16 bits should be
> plenty. Redefine it to unsigned short, making room for order as unsigned
> short in follow up commit.
>
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>

Looks good.
Reviewed-by: Pankaj Raghav <p.raghav@samsung.com>

> ---
> include/linux/fs.h | 2 +-
> mm/filemap.c | 11 ++++++-----
> 2 files changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 016b0fe1536e..44362bef0010 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1042,7 +1042,7 @@ struct file_ra_state {
> unsigned int size;
> unsigned int async_size;
> unsigned int ra_pages;
> - unsigned int mmap_miss;
> + unsigned short mmap_miss;
> loff_t prev_pos;
> };
>
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 7b90cbeb4a1a..fa129ecfd80f 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -3207,7 +3207,7 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf)
> DEFINE_READAHEAD(ractl, file, ra, mapping, vmf->pgoff);
> struct file *fpin = NULL;
> unsigned long vm_flags = vmf->vma->vm_flags;
> - unsigned int mmap_miss;
> + unsigned short mmap_miss;
>
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> /* Use the readahead code, even if readahead is disabled */
> @@ -3275,7 +3275,7 @@ static struct file *do_async_mmap_readahead(struct vm_fault *vmf,
> struct file_ra_state *ra = &file->f_ra;
> DEFINE_READAHEAD(ractl, file, ra, file->f_mapping, vmf->pgoff);
> struct file *fpin = NULL;
> - unsigned int mmap_miss;
> + unsigned short mmap_miss;
>
> /* If we don't want any read-ahead, don't bother */
> if (vmf->vma->vm_flags & VM_RAND_READ || !ra->ra_pages)
> @@ -3595,7 +3595,7 @@ static struct folio *next_uptodate_folio(struct xa_state *xas,
> static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
> struct folio *folio, unsigned long start,
> unsigned long addr, unsigned int nr_pages,
> - unsigned long *rss, unsigned int *mmap_miss)
> + unsigned long *rss, unsigned short *mmap_miss)
> {
> vm_fault_t ret = 0;
> struct page *page = folio_page(folio, start);
> @@ -3657,7 +3657,7 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
>
> static vm_fault_t filemap_map_order0_folio(struct vm_fault *vmf,
> struct folio *folio, unsigned long addr,
> - unsigned long *rss, unsigned int *mmap_miss)
> + unsigned long *rss, unsigned short *mmap_miss)
> {
> vm_fault_t ret = 0;
> struct page *page = &folio->page;
> @@ -3699,7 +3699,8 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
> struct folio *folio;
> vm_fault_t ret = 0;
> unsigned long rss = 0;
> - unsigned int nr_pages = 0, mmap_miss = 0, mmap_miss_saved, folio_type;
> + unsigned int nr_pages = 0, folio_type;
> + unsigned short mmap_miss = 0, mmap_miss_saved;
>
> rcu_read_lock();
> folio = next_uptodate_folio(&xas, mapping, end_pgoff);
> --
> 2.43.0
>