[RFC 6/8] shmem: consider block size in shmem_default_max_inodes()

[Luis Chamberlain <mcgrof@kernel.org>]

Today we allow for a max number of inodes in consideration for
the smallest possible inodes with just one block of size PAGE_SIZE.
The max number of inodes depend on the size of the block size then,
and if we want to support higher block sizes we end up with less
number of inodes.

Account for this in the computation for the max number of inodes.

If the blocksize is greater than the PAGE_SIZE, we simply divide the
number of pages usable, multiply by the page size and divide by the
blocksize.

This produces no functional changes right now as we don't support
larger block sizes yet.

Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
---
 mm/shmem.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index b83596467706..5a64efd1f3c2 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -143,11 +143,14 @@ static unsigned long shmem_default_max_blocks(u64 blocksize)
 	return totalram_pages() >> (__ffs(blocksize) - PAGE_SHIFT + 1);
 }
 
-static unsigned long shmem_default_max_inodes(void)
+static unsigned long shmem_default_max_inodes(u64 blocksize)
 {
 	unsigned long nr_pages = totalram_pages();
+	unsigned long pages_for_inodes = min(nr_pages - totalhigh_pages(), nr_pages / 2);
 
-	return min(nr_pages - totalhigh_pages(), nr_pages / 2);
+	if (blocksize == shmem_default_bsize())
+		return pages_for_inodes;
+	return pages_for_inodes >> (__ffs(blocksize) - PAGE_SHIFT);
 }
 #else
 static u64 shmem_sb_blocksize(struct shmem_sb_info *sbinfo)
@@ -4028,7 +4031,7 @@ static int shmem_show_options(struct seq_file *seq, struct dentry *root)
 	if (sbinfo->max_blocks != shmem_default_max_blocks(shmem_default_bsize()))
 		seq_printf(seq, ",size=%luk",
 			sbinfo->max_blocks << (PAGE_SHIFT - 10));
-	if (sbinfo->max_inodes != shmem_default_max_inodes())
+	if (sbinfo->max_inodes != shmem_default_max_inodes(shmem_default_bsize()))
 		seq_printf(seq, ",nr_inodes=%lu", sbinfo->max_inodes);
 	if (sbinfo->mode != (0777 | S_ISVTX))
 		seq_printf(seq, ",mode=%03ho", sbinfo->mode);
@@ -4109,7 +4112,7 @@ static int shmem_fill_super(struct super_block *sb, struct fs_context *fc)
 		if (!(ctx->seen & SHMEM_SEEN_BLOCKS))
 			ctx->blocks = shmem_default_max_blocks(shmem_default_bsize());
 		if (!(ctx->seen & SHMEM_SEEN_INODES))
-			ctx->inodes = shmem_default_max_inodes();
+			ctx->inodes = shmem_default_max_inodes(shmem_default_bsize());
 		if (!(ctx->seen & SHMEM_SEEN_INUMS))
 			ctx->full_inums = IS_ENABLED(CONFIG_TMPFS_INODE64);
 		sbinfo->noswap = ctx->noswap;
-- 
2.39.2