linux-kernel - Re: [PATCH 2/2] fuse: Adjust readdir() buffer to requesting buffer size.

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Message-ID: <CAJfpegtOGWz_r=7dbQiCh2wqjKh59BqzqJ0ruhtYtsYBB+GG2Q@mail.gmail.com>
Date: Tue, 1 Apr 2025 16:40:00 +0200
From: Miklos Szeredi <miklos@...redi.hu>
To: Jaco Kroon <jaco@....co.za>
Cc: bernd.schubert@...tmail.fm, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, christophe.jaillet@...adoo.fr, 
	joannelkoong@...il.com, rdunlap@...radead.org, trapexit@...wn.link, 
	david.laight.linux@...il.com
Subject: Re: [PATCH 2/2] fuse: Adjust readdir() buffer to requesting buffer size.

On Tue, 1 Apr 2025 at 16:29, Jaco Kroon <jaco@....co.za> wrote:
> After:
>
> getdents64(3, 0x7ffae8eed040 /* 276 entries */, 131072) = 6696
> getdents64(3, 0x7ffae8eed040 /* 0 entries */, 131072) = 0

This looks great.  But see below.

>
> Signed-off-by: Jaco Kroon <jaco@....co.za>
> ---
>  fs/fuse/readdir.c | 19 +++++++++++++++----
>  1 file changed, 15 insertions(+), 4 deletions(-)
>
> diff --git a/fs/fuse/readdir.c b/fs/fuse/readdir.c
> index 17ce9636a2b1..a13534f411b4 100644
> --- a/fs/fuse/readdir.c
> +++ b/fs/fuse/readdir.c
> @@ -12,6 +12,7 @@
>  #include <linux/posix_acl.h>
>  #include <linux/pagemap.h>
>  #include <linux/highmem.h>
> +#include <linux/minmax.h>
>
>  static bool fuse_use_readdirplus(struct inode *dir, struct dir_context *ctx)
>  {
> @@ -337,11 +338,21 @@ static int fuse_readdir_uncached(struct file *file, struct dir_context *ctx)
>         struct fuse_mount *fm = get_fuse_mount(inode);
>         struct fuse_io_args ia = {};
>         struct fuse_args_pages *ap = &ia.ap;
> -       struct fuse_folio_desc desc = { .length = PAGE_SIZE };
> +       struct fuse_folio_desc desc = { .length = ctx->count };
>         u64 attr_version = 0, evict_ctr = 0;
>         bool locked;
> +       int order;
>
> -       folio = folio_alloc(GFP_KERNEL, 0);
> +       desc.length = clamp(desc.length, PAGE_SIZE, fm->fc->max_pages << PAGE_SHIFT);
> +       order = get_count_order(desc.length >> CONFIG_PAGE_SHIFT);
> +
> +       do {
> +               folio = folio_alloc(GFP_KERNEL, order);
> +               if (folio)
> +                       break;
> +               --order;
> +               desc.length = PAGE_SIZE << order;
> +       } while (order >= 0);
>         if (!folio)
>                 return -ENOMEM;

Why not use kvmalloc instead?

We could also implement allocation based on size of result in dev.c to
optimize this, as most directories will be small, but that can be done
later.

Thanks,
Miklos