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

[Jaco Kroon <jaco@xxxxxxxxx>]

Clamp to min 1 page (4KB) and max 128 pages (512KB).

Glusterfs trial using strace ls -l.

Before:

getdents64(3, 0x7f2d7d7a7040 /* 25 entries */, 131072) = 600
getdents64(3, 0x7f2d7d7a7040 /* 25 entries */, 131072) = 616
getdents64(3, 0x7f2d7d7a7040 /* 25 entries */, 131072) = 624
getdents64(3, 0x7f2d7d7a7040 /* 25 entries */, 131072) = 600
getdents64(3, 0x7f2d7d7a7040 /* 25 entries */, 131072) = 600
getdents64(3, 0x7f2d7d7a7040 /* 25 entries */, 131072) = 624
getdents64(3, 0x7f2d7d7a7040 /* 25 entries */, 131072) = 600
getdents64(3, 0x7f2d7d7a7040 /* 25 entries */, 131072) = 600
getdents64(3, 0x7f2d7d7a7040 /* 25 entries */, 131072) = 600
getdents64(3, 0x7f2d7d7a7040 /* 25 entries */, 131072) = 600
getdents64(3, 0x7f2d7d7a7040 /* 25 entries */, 131072) = 608
getdents64(3, 0x7f2d7d7a7040 /* 1 entries */, 131072) = 24
getdents64(3, 0x7f2d7d7a7040 /* 0 entries */, 131072) = 0

After:

getdents64(3, 0x7ffae8eed040 /* 276 entries */, 131072) = 6696
getdents64(3, 0x7ffae8eed040 /* 0 entries */, 131072) = 0

Signed-off-by: Jaco Kroon <jaco@xxxxxxxxx>
---
 fs/fuse/readdir.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/fs/fuse/readdir.c b/fs/fuse/readdir.c
index 17ce9636a2b1..a0ccbc84b000 100644
--- a/fs/fuse/readdir.c
+++ b/fs/fuse/readdir.c
@@ -337,11 +337,25 @@ 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);
+	if (desc.length < PAGE_SIZE)
+		desc.length = PAGE_SIZE;
+	else if (desc.length > (PAGE_SIZE << 7)) /* 128 pages, typically 512KB */
+		desc.length = PAGE_SIZE << 7;
+
+	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;
 
@@ -353,10 +367,10 @@ static int fuse_readdir_uncached(struct file *file, struct dir_context *ctx)
 	if (plus) {
 		attr_version = fuse_get_attr_version(fm->fc);
 		evict_ctr = fuse_get_evict_ctr(fm->fc);
-		fuse_read_args_fill(&ia, file, ctx->pos, PAGE_SIZE,
+		fuse_read_args_fill(&ia, file, ctx->pos, desc.length,
 				    FUSE_READDIRPLUS);
 	} else {
-		fuse_read_args_fill(&ia, file, ctx->pos, PAGE_SIZE,
+		fuse_read_args_fill(&ia, file, ctx->pos, desc.length,
 				    FUSE_READDIR);
 	}
 	locked = fuse_lock_inode(inode);
-- 
2.48.1