linux-kernel - [PATCH 1/8] shmem: shrink shmem_inode_info: dir

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Message-ID: <86ebb4b-c571-b9e8-27f5-cb82ec50357e@google.com>
Date:   Fri, 29 Sep 2023 20:25:38 -0700 (PDT)
From:   Hugh Dickins <hughd@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
cc:     Christian Brauner <brauner@...nel.org>,
        Carlos Maiolino <cem@...nel.org>,
        Chuck Lever <chuck.lever@...cle.com>, Jan Kara <jack@...e.cz>,
        Matthew Wilcox <willy@...radead.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: [PATCH 1/8] shmem: shrink shmem_inode_info: dir_offsets in a union

Shave 32 bytes off (the 64-bit) shmem_inode_info.  There was a 4-byte
pahole after stop_eviction, better filled by fsflags.  And the 24-byte
dir_offsets can only be used by directories, whereas shrinklist and
swaplist only by shmem_mapping() inodes (regular files or long symlinks):
so put those into a union.  No change in mm/shmem.c is required for this.

Signed-off-by: Hugh Dickins <hughd@...gle.com>
---
 include/linux/shmem_fs.h | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index 6b0c626620f5..2caa6b86106a 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -23,18 +23,22 @@ struct shmem_inode_info {
 	unsigned long		flags;
 	unsigned long		alloced;	/* data pages alloced to file */
 	unsigned long		swapped;	/* subtotal assigned to swap */
-	pgoff_t			fallocend;	/* highest fallocate endindex */
-	struct list_head        shrinklist;     /* shrinkable hpage inodes */
-	struct list_head	swaplist;	/* chain of maybes on swap */
+	union {
+	    struct offset_ctx	dir_offsets;	/* stable directory offsets */
+	    struct {
+		struct list_head shrinklist;	/* shrinkable hpage inodes */
+		struct list_head swaplist;	/* chain of maybes on swap */
+	    };
+	};
+	struct timespec64	i_crtime;	/* file creation time */
 	struct shared_policy	policy;		/* NUMA memory alloc policy */
 	struct simple_xattrs	xattrs;		/* list of xattrs */
+	pgoff_t			fallocend;	/* highest fallocate endindex */
+	unsigned int		fsflags;	/* for FS_IOC_[SG]ETFLAGS */
 	atomic_t		stop_eviction;	/* hold when working on inode */
-	struct timespec64	i_crtime;	/* file creation time */
-	unsigned int		fsflags;	/* flags for FS_IOC_[SG]ETFLAGS */
 #ifdef CONFIG_TMPFS_QUOTA
 	struct dquot		*i_dquot[MAXQUOTAS];
 #endif
-	struct offset_ctx	dir_offsets;	/* stable entry offsets */
 	struct inode		vfs_inode;
 };
 
-- 
2.35.3