From patchwork Thu Oct 24 17:31:10 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Sterba X-Patchwork-Id: 11210553 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id C998E139A for ; Thu, 24 Oct 2019 17:31:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B18AF20650 for ; Thu, 24 Oct 2019 17:31:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732485AbfJXRbB (ORCPT ); Thu, 24 Oct 2019 13:31:01 -0400 Received: from mx2.suse.de ([195.135.220.15]:47282 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1729458AbfJXRbB (ORCPT ); Thu, 24 Oct 2019 13:31:01 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 59819B0DA; Thu, 24 Oct 2019 17:30:59 +0000 (UTC) Received: by ds.suse.cz (Postfix, from userid 10065) id 2C231DA733; Thu, 24 Oct 2019 19:31:11 +0200 (CEST) From: David Sterba To: linux-block@vger.kernel.org Cc: David Sterba Subject: [PATCH] block: reorder bio::__bi_remaining for better packing Date: Thu, 24 Oct 2019 19:31:10 +0200 Message-Id: X-Mailer: git-send-email 2.23.0 MIME-Version: 1.0 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Simple reordering of __bi_remaining can reduce bio size by 8 bytes that are now wasted on padding (measured on x86_64): struct bio { struct bio * bi_next; /* 0 8 */ struct gendisk * bi_disk; /* 8 8 */ unsigned int bi_opf; /* 16 4 */ short unsigned int bi_flags; /* 20 2 */ short unsigned int bi_ioprio; /* 22 2 */ short unsigned int bi_write_hint; /* 24 2 */ blk_status_t bi_status; /* 26 1 */ u8 bi_partno; /* 27 1 */ /* XXX 4 bytes hole, try to pack */ struct bvec_iter bi_iter; /* 32 24 */ /* XXX last struct has 4 bytes of padding */ atomic_t __bi_remaining; /* 56 4 */ /* XXX 4 bytes hole, try to pack */ [...] /* size: 104, cachelines: 2, members: 19 */ /* sum members: 96, holes: 2, sum holes: 8 */ /* paddings: 1, sum paddings: 4 */ /* last cacheline: 40 bytes */ }; Now becomes: struct bio { struct bio * bi_next; /* 0 8 */ struct gendisk * bi_disk; /* 8 8 */ unsigned int bi_opf; /* 16 4 */ short unsigned int bi_flags; /* 20 2 */ short unsigned int bi_ioprio; /* 22 2 */ short unsigned int bi_write_hint; /* 24 2 */ blk_status_t bi_status; /* 26 1 */ u8 bi_partno; /* 27 1 */ atomic_t __bi_remaining; /* 28 4 */ struct bvec_iter bi_iter; /* 32 24 */ /* XXX last struct has 4 bytes of padding */ [...] /* size: 96, cachelines: 2, members: 19 */ /* paddings: 1, sum paddings: 4 */ /* last cacheline: 32 bytes */ }; Signed-off-by: David Sterba --- include/linux/blk_types.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h index d688b96d1d63..1e7eeec16458 100644 --- a/include/linux/blk_types.h +++ b/include/linux/blk_types.h @@ -153,10 +153,10 @@ struct bio { unsigned short bi_write_hint; blk_status_t bi_status; u8 bi_partno; + atomic_t __bi_remaining; struct bvec_iter bi_iter; - atomic_t __bi_remaining; bio_end_io_t *bi_end_io; void *bi_private;