Re: [PATCH v2 2/3] ntfs: avoid heap allocation for free-cluster readahead state

[Hyunchul Lee]

2026년 5월 21일 (목) 오후 7:18, DaeMyung Kang <charsyam@xxxxxxxxx>님이 작성:
>
> get_nr_free_clusters() is run from the precalc_free_clusters() worker
> queued at the end of ntfs_fill_super().  It is also the only place that
> publishes the result by atomic64_set(&vol->free_clusters, ...), sets
> NVolSetFreeClusterKnown(), and wakes vol->free_waitq.
>
> The function currently allocates a temporary file_ra_state with
> kzalloc() before that publication happens.  If the allocation fails,
> get_nr_free_clusters() returns 0 without setting NVolFreeClusterKnown()
> or waking vol->free_waitq, so callers that wait for the free count can
> block forever.
>
> The readahead state is only used synchronously while scanning the bitmap
> and struct file_ra_state is small.  Keep it on the stack and pass it to
> the readahead helper by address, eliminating the early allocation
> failure path.  Zero-initialize the on-stack state because
> file_ra_state_init() only sets ra_pages and prev_pos.
>
> Signed-off-by: DaeMyung Kang <charsyam@xxxxxxxxx>
> ---
>  fs/ntfs/super.c | 11 +++--------
>  1 file changed, 3 insertions(+), 8 deletions(-)
>
> diff --git a/fs/ntfs/super.c b/fs/ntfs/super.c
> index 7e3561265b47..14fd244f29fe 100644
> --- a/fs/ntfs/super.c
> +++ b/fs/ntfs/super.c
> @@ -1954,7 +1954,7 @@ s64 get_nr_free_clusters(struct ntfs_volume *vol)
>         struct address_space *mapping = vol->lcnbmp_ino->i_mapping;
>         struct folio *folio;
>         pgoff_t index, max_index;
> -       struct file_ra_state *ra;
> +       struct file_ra_state ra = {};
>
>         ntfs_debug("Entering.");
>         /* Serialize accesses to the cluster bitmap. */
> @@ -1962,11 +1962,7 @@ s64 get_nr_free_clusters(struct ntfs_volume *vol)
>         if (NVolFreeClusterKnown(vol))
>                 return atomic64_read(&vol->free_clusters);
>
> -       ra = kzalloc(sizeof(*ra), GFP_NOFS);
> -       if (!ra)
> -               return 0;
> -
> -       file_ra_state_init(ra, mapping);
> +       file_ra_state_init(&ra, mapping);
>
>         /*
>          * Convert the number of bits into bytes rounded up, then convert into
> @@ -1985,7 +1981,7 @@ s64 get_nr_free_clusters(struct ntfs_volume *vol)
>                  * Get folio from page cache, getting it from backing store
>                  * if necessary, and increment the use count.
>                  */
> -               folio = ntfs_get_locked_folio(mapping, index, max_index, ra);
> +               folio = ntfs_get_locked_folio(mapping, index, max_index, &ra);

This line modifies the __get_nr_free_mft_records function, not the
get_nr_free_clusters function.
Therefore the patch needs to be rebased on ntfs-next branch at
git://git.kernel.org/pub/scm/linux/kernel/git/linkinjeon/ntfs.git.

>
>                 /* Ignore pages which errored synchronously. */
>                 if (IS_ERR(folio)) {
> @@ -2024,7 +2020,6 @@ s64 get_nr_free_clusters(struct ntfs_volume *vol)
>         else
>                 atomic64_set(&vol->free_clusters, nr_free);
>
> -       kfree(ra);
>         NVolSetFreeClusterKnown(vol);
>         wake_up_all(&vol->free_waitq);
>         ntfs_debug("Exiting.");
> --
> 2.43.0
>


-- 
Thanks,
Hyunchul