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Tsirkin" , Jason Wang Cc: linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org, Christophe JAILLET , virtualization@lists.linux-foundation.org Subject: [PATCH] virtio: Reorder fields in 'struct virtqueue' Date: Sat, 18 Feb 2023 09:10:31 +0100 Message-Id: <8f3d2e49270a2158717e15008e7ed7228196ba02.1676707807.git.christophe.jaillet@wanadoo.fr> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1758157154702862341?= X-GMAIL-MSGID: =?utf-8?q?1758157154702862341?= Group some variables based on their sizes to reduce hole and avoid padding. On x86_64, this shrinks the size of 'struct virtqueue' from 72 to 68 bytes. It saves a few bytes of memory. Signed-off-by: Christophe JAILLET Acked-by: Peter Lafreniere Reviewed-by: Stefano Garzarella --- Using pahole Before: ====== struct virtqueue { struct list_head list; /* 0 16 */ void (*callback)(struct virtqueue *); /* 16 8 */ const char * name; /* 24 8 */ struct virtio_device * vdev; /* 32 8 */ unsigned int index; /* 40 4 */ unsigned int num_free; /* 44 4 */ unsigned int num_max; /* 48 4 */ /* XXX 4 bytes hole, try to pack */ void * priv; /* 56 8 */ /* --- cacheline 1 boundary (64 bytes) --- */ bool reset; /* 64 1 */ /* size: 72, cachelines: 2, members: 9 */ /* sum members: 61, holes: 1, sum holes: 4 */ /* padding: 7 */ /* last cacheline: 8 bytes */ }; After: ===== struct virtqueue { struct list_head list; /* 0 16 */ void (*callback)(struct virtqueue *); /* 16 8 */ const char * name; /* 24 8 */ struct virtio_device * vdev; /* 32 8 */ unsigned int index; /* 40 4 */ unsigned int num_free; /* 44 4 */ unsigned int num_max; /* 48 4 */ bool reset; /* 52 1 */ /* XXX 3 bytes hole, try to pack */ void * priv; /* 56 8 */ /* size: 64, cachelines: 1, members: 9 */ /* sum members: 61, holes: 1, sum holes: 3 */ }; --- include/linux/virtio.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/virtio.h b/include/linux/virtio.h index 6ac2655500dc..9439ae898310 100644 --- a/include/linux/virtio.h +++ b/include/linux/virtio.h @@ -35,8 +35,8 @@ struct virtqueue { unsigned int index; unsigned int num_free; unsigned int num_max; - void *priv; bool reset; + void *priv; }; int virtqueue_add_outbuf(struct virtqueue *vq,