From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from firstgate.proxmox.com (firstgate.proxmox.com [IPv6:2a01:7e0:0:424::9]) by lore.proxmox.com (Postfix) with ESMTPS id EB9121FF16B for ; Mon, 30 Sep 2024 13:41:06 +0200 (CEST) Received: from firstgate.proxmox.com (localhost [127.0.0.1]) by firstgate.proxmox.com (Proxmox) with ESMTP id 025B415ACE; Mon, 30 Sep 2024 13:41:24 +0200 (CEST) From: Filip Schauer To: pve-devel@lists.proxmox.com Date: Mon, 30 Sep 2024 13:40:45 +0200 Message-Id: <20240930114045.76730-1-f.schauer@proxmox.com> X-Mailer: git-send-email 2.39.5 MIME-Version: 1.0 X-SPAM-LEVEL: Spam detection results: 0 AWL -0.050 Adjusted score from AWL reputation of From: address BAYES_00 -1.9 Bayes spam probability is 0 to 1% DMARC_MISSING 0.1 Missing DMARC policy KAM_DMARC_STATUS 0.01 Test Rule for DKIM or SPF Failure with Strict Alignment RCVD_IN_VALIDITY_CERTIFIED_BLOCKED 0.001 ADMINISTRATOR NOTICE: The query to Validity was blocked. See https://knowledge.validity.com/hc/en-us/articles/20961730681243 for more information. RCVD_IN_VALIDITY_RPBL_BLOCKED 0.001 ADMINISTRATOR NOTICE: The query to Validity was blocked. See https://knowledge.validity.com/hc/en-us/articles/20961730681243 for more information. RCVD_IN_VALIDITY_SAFE_BLOCKED 0.001 ADMINISTRATOR NOTICE: The query to Validity was blocked. See https://knowledge.validity.com/hc/en-us/articles/20961730681243 for more information. SPF_HELO_NONE 0.001 SPF: HELO does not publish an SPF Record SPF_PASS -0.001 SPF: sender matches SPF record Subject: [pve-devel] [PATCH v2 common] tools: file_set_contents: use syswrite instead of print X-BeenThere: pve-devel@lists.proxmox.com X-Mailman-Version: 2.1.29 Precedence: list List-Id: Proxmox VE development discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Proxmox VE development discussion Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: pve-devel-bounces@lists.proxmox.com Sender: "pve-devel" The use of `print` can be inefficient for writing larger files due to its default buffering in 8 KiB blocks. This is especially problematic on `pmxcfs` where files are written in 4 KiB blocks due to the defaults of `libfuse2`. This leads to significant write amplification on files larger than 4 KiB. Patch (fix #5728: pmxcfs: allow bigger writes than 4k for fuse) [1] addresses this by enabling `big_writes`, allowing up to 128 KiB blocks. But due to the use of `print` in `file_set_contents`, writes are still only buffered in 8 KiB blocks. To further address this, this commit switches to using `syswrite` instead of `print` to mitigate the block size limit imposed by `print`. Combined with patch [1], file writes to `/etc/pve/` are now buffered in 128 KiB blocks. The table below illustrates the drastic reduction in write amplification when writing files of different sizes to `/etc/pve/` using `file_set_contents`: print big_writes+print big_writes+syswrite file size written amplif. written amplif. written amplif. 1 KiB 48 KiB 48.0 45 KiB 45.0 41 KiB 41.0 2 KiB 48 KiB 24.0 45 KiB 22.5 62 KiB 31.0 4 KiB 82 KiB 20.5 80 KiB 20.0 73 KiB 18.3 8 KiB 121 KiB 15.1 90 KiB 11.3 89 KiB 11.1 16 KiB 217 KiB 13.6 146 KiB 9.1 113 KiB 7.1 32 KiB 506 KiB 15.8 314 KiB 9.8 158 KiB 4.9 64 KiB 1472 KiB 23.0 826 KiB 12.9 259 KiB 4.0 128 KiB 5585 KiB 43.6 3765 KiB 29.4 452 KiB 3.5 256 KiB 20424 KiB 79.8 10743 KiB 42.0 2351 KiB 9.2 512 KiB 86715 KiB 169.4 43650 KiB 85.3 3204 KiB 6.3 1024 KiB 369568 KiB 360.9 187496 KiB 183.1 15845 KiB 15.5 Since `file_set_contents` also performs a `rename` after writing, the following table shows the results when the file is written without renaming it afterwards: print big_writes+print big_writes+syswrite file size written amplif. written amplif. written amplif. 1 KiB 29 KiB 29.0 29 KiB 29.0 25 KiB 25.0 2 KiB 29 KiB 14.5 30 KiB 15.0 25 KiB 12.5 4 KiB 37 KiB 9.3 44 KiB 11.0 41 KiB 10.3 8 KiB 61 KiB 7.6 45 KiB 5.6 45 KiB 5.6 16 KiB 143 KiB 8.9 86 KiB 5.4 57 KiB 3.6 32 KiB 396 KiB 12.4 225 KiB 7.0 69 KiB 2.2 64 KiB 1281 KiB 20.0 673 KiB 10.5 105 KiB 1.6 128 KiB 4789 KiB 37.4 3478 KiB 27.2 169 KiB 1.3 256 KiB 18868 KiB 73.7 9976 KiB 39.0 572 KiB 2.2 512 KiB 79304 KiB 154.9 42714 KiB 83.4 2150 KiB 4.2 1024 KiB 347929 KiB 339.8 182483 KiB 178.2 11133 KiB 10.9 [1] https://lists.proxmox.com/pipermail/pve-devel/2024-September/065396.html Signed-off-by: Filip Schauer --- Changes since v1: * Add benchmark results without rename to commit message * Fix "Wide character in syswrite" error by first encoding $data with print src/PVE/Tools.pm | 21 ++++++++++++++++++--- 1 file changed, 18 insertions(+), 3 deletions(-) diff --git a/src/PVE/Tools.pm b/src/PVE/Tools.pm index bd305bd..e4ff7f9 100644 --- a/src/PVE/Tools.pm +++ b/src/PVE/Tools.pm @@ -285,10 +285,25 @@ sub file_set_contents { } die "unable to open file '$tmpname' - $!\n" if !$fh; - binmode($fh, ":encoding(UTF-8)") if $force_utf8; + if ($force_utf8) { + $data = encode("utf8", $data); + } else { + # Encode wide characters with print before passing them to syswrite + my $unencoded_data = $data; + open my $datafh, '>', \$data; + print $datafh $unencoded_data; + close $datafh; + } + + my $offset = 0; + my $len = length($data); + + while ($offset < $len) { + $offset += syswrite($fh, $data, $len - $offset, $offset) + or die "unable to write '$tmpname' - $!\n"; + } - die "unable to write '$tmpname' - $!\n" unless print $fh $data; - die "closing file '$tmpname' failed - $!\n" unless close $fh; + close $fh or die "closing file '$tmpname' failed - $!\n"; }; my $err = $@; -- 2.39.5 _______________________________________________ pve-devel mailing list pve-devel@lists.proxmox.com https://lists.proxmox.com/cgi-bin/mailman/listinfo/pve-devel