Re: [PATCH 03/40] fs: Convert alloc_inode_sb() to a macro

On Tue, May 02, 2023 at 02:35:30PM +0200, Petr Tesařík wrote:

On Mon,  1 May 2023 09:54:13 -0700
Suren Baghdasaryan [off-list ref] wrote:

quoted

From: Kent Overstreet <kent.overstreet@linux.dev>

We're introducing alloc tagging, which tracks memory allocations by
callsite. Converting alloc_inode_sb() to a macro means allocations will
be tracked by its caller, which is a bit more useful.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
---
 include/linux/fs.h | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 21a981680856..4905ce14db0b 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h

@@ -2699,11 +2699,7 @@ int setattr_should_drop_sgid(struct mnt_idmap *idmap,
  * This must be used for allocating filesystems specific inodes to set
  * up the inode reclaim context correctly.
  */
-static inline void *
-alloc_inode_sb(struct super_block *sb, struct kmem_cache *cache, gfp_t gfp)
-{
-	return kmem_cache_alloc_lru(cache, &sb->s_inode_lru, gfp);
-}
+#define alloc_inode_sb(_sb, _cache, _gfp) kmem_cache_alloc_lru(_cache, &_sb->s_inode_lru, _gfp)

Honestly, I don't like this change. In general, pre-processor macros
are ugly and error-prone.

It's a one line macro, it's fine.

Besides, it works for you only because __kmem_cache_alloc_lru() is
declared __always_inline (unless CONFIG_SLUB_TINY is defined, but then
you probably don't want the tracking either). In any case, it's going
to be difficult for people to understand why and how this works.

I think you must be confused. kmem_cache_alloc_lru() is a macro, and we
need that macro to be expanded at the alloc_inode_sb() callsite. It's
got nothing to do with whether or not __kmem_cache_alloc_lru() is inline
or not.

If the actual caller of alloc_inode_sb() is needed, I'd rather add it
as a parameter and pass down _RET_IP_ explicitly here.

That approach was considered, but adding an ip parameter to every memory
allocation function would've been far more churn.