ext4 crypto: shrink size of the ext4_crypto_ctx structure

Some fields are only used when the crypto_ctx is being used on the
read path, some are only used on the write path, and some are only
used when the structure is on free list.  Optimize memory use by using
a union.
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/crypto.c

@@ -71,14 +71,14 @@ void ext4_release_crypto_ctx(struct ext4_crypto_ctx *ctx)
 {
 	unsigned long flags;
 
-	if (ctx->bounce_page) {
+	if (ctx->flags & EXT4_WRITE_PATH_FL && ctx->w.bounce_page) {
 		if (ctx->flags & EXT4_BOUNCE_PAGE_REQUIRES_FREE_ENCRYPT_FL)
-			__free_page(ctx->bounce_page);
+			__free_page(ctx->w.bounce_page);
 		else
-			mempool_free(ctx->bounce_page, ext4_bounce_page_pool);
-		ctx->bounce_page = NULL;
+			mempool_free(ctx->w.bounce_page, ext4_bounce_page_pool);
 	}
-	ctx->control_page = NULL;
+	ctx->w.bounce_page = NULL;
+	ctx->w.control_page = NULL;
 	if (ctx->flags & EXT4_CTX_REQUIRES_FREE_ENCRYPT_FL) {
 		if (ctx->tfm)
 			crypto_free_tfm(ctx->tfm);
@@ -134,6 +134,7 @@ struct ext4_crypto_ctx *ext4_get_crypto_ctx(struct inode *inode)
 	} else {
 		ctx->flags &= ~EXT4_CTX_REQUIRES_FREE_ENCRYPT_FL;
 	}
+	ctx->flags &= ~EXT4_WRITE_PATH_FL;
 
 	/* Allocate a new Crypto API context if we don't already have
 	 * one or if it isn't the right mode. */
@@ -165,10 +166,6 @@ struct ext4_crypto_ctx *ext4_get_crypto_ctx(struct inode *inode)
 	}
 	BUG_ON(ci->ci_size != ext4_encryption_key_size(ci->ci_data_mode));
 
-	/* There shouldn't be a bounce page attached to the crypto
-	 * context at this point. */
-	BUG_ON(ctx->bounce_page);
-
 out:
 	if (res) {
 		if (!IS_ERR_OR_NULL(ctx))
@@ -189,15 +186,6 @@ void ext4_exit_crypto(void)
 	struct ext4_crypto_ctx *pos, *n;
 
 	list_for_each_entry_safe(pos, n, &ext4_free_crypto_ctxs, free_list) {
-		if (pos->bounce_page) {
-			if (pos->flags &
-			    EXT4_BOUNCE_PAGE_REQUIRES_FREE_ENCRYPT_FL) {
-				__free_page(pos->bounce_page);
-			} else {
-				mempool_free(pos->bounce_page,
-					     ext4_bounce_page_pool);
-			}
-		}
 		if (pos->tfm)
 			crypto_free_tfm(pos->tfm);
 		kmem_cache_free(ext4_crypto_ctx_cachep, pos);
@@ -425,8 +413,9 @@ struct page *ext4_encrypt(struct inode *inode,
 	} else {
 		ctx->flags |= EXT4_BOUNCE_PAGE_REQUIRES_FREE_ENCRYPT_FL;
 	}
-	ctx->bounce_page = ciphertext_page;
-	ctx->control_page = plaintext_page;
+	ctx->flags |= EXT4_WRITE_PATH_FL;
+	ctx->w.bounce_page = ciphertext_page;
+	ctx->w.control_page = plaintext_page;
 	err = ext4_page_crypto(ctx, inode, EXT4_ENCRYPT, plaintext_page->index,
 			       plaintext_page, ciphertext_page);
 	if (err) {
@@ -505,7 +494,7 @@ int ext4_encrypted_zeroout(struct inode *inode, struct ext4_extent *ex)
 	} else {
 		ctx->flags |= EXT4_BOUNCE_PAGE_REQUIRES_FREE_ENCRYPT_FL;
 	}
-	ctx->bounce_page = ciphertext_page;
+	ctx->w.bounce_page = ciphertext_page;
 
 	while (len--) {
 		err = ext4_page_crypto(ctx, inode, EXT4_ENCRYPT, lblk,

fs/ext4/ext4_crypto.h

@@ -86,16 +86,23 @@ struct ext4_crypt_info {
 
 #define EXT4_CTX_REQUIRES_FREE_ENCRYPT_FL             0x00000001
 #define EXT4_BOUNCE_PAGE_REQUIRES_FREE_ENCRYPT_FL     0x00000002
+#define EXT4_WRITE_PATH_FL			      0x00000004
 
 struct ext4_crypto_ctx {
 	struct crypto_tfm *tfm;         /* Crypto API context */
-	struct page *bounce_page;       /* Ciphertext page on write path */
-	struct page *control_page;      /* Original page on write path */
-	struct bio *bio;                /* The bio for this context */
-	struct work_struct work;        /* Work queue for read complete path */
-	struct list_head free_list;     /* Free list */
-	int flags;                      /* Flags */
-	int mode;                       /* Encryption mode for tfm */
+	union {
+		struct {
+			struct page *bounce_page;       /* Ciphertext page */
+			struct page *control_page;      /* Original page  */
+		} w;
+		struct {
+			struct bio *bio;
+			struct work_struct work;
+		} r;
+		struct list_head free_list;     /* Free list */
+	};
+	char flags;                      /* Flags */
+	char mode;                       /* Encryption mode for tfm */
 };
 
 struct ext4_completion_result {

fs/ext4/page-io.c

@@ -84,7 +84,7 @@ static void ext4_finish_bio(struct bio *bio)
 			/* The bounce data pages are unmapped. */
 			data_page = page;
 			ctx = (struct ext4_crypto_ctx *)page_private(data_page);
-			page = ctx->control_page;
+			page = ctx->w.control_page;
 		}
 #endif
 

fs/ext4/readpage.c

@@ -54,8 +54,8 @@ static void completion_pages(struct work_struct *work)
 {
 #ifdef CONFIG_EXT4_FS_ENCRYPTION
 	struct ext4_crypto_ctx *ctx =
-		container_of(work, struct ext4_crypto_ctx, work);
-	struct bio	*bio	= ctx->bio;
+		container_of(work, struct ext4_crypto_ctx, r.work);
+	struct bio	*bio	= ctx->r.bio;
 	struct bio_vec	*bv;
 	int		i;
 
@@ -109,9 +109,9 @@ static void mpage_end_io(struct bio *bio, int err)
 		if (err) {
 			ext4_release_crypto_ctx(ctx);
 		} else {
-			INIT_WORK(&ctx->work, completion_pages);
-			ctx->bio = bio;
-			queue_work(ext4_read_workqueue, &ctx->work);
+			INIT_WORK(&ctx->r.work, completion_pages);
+			ctx->r.bio = bio;
+			queue_work(ext4_read_workqueue, &ctx->r.work);
 			return;
 		}
 	}