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899fabb26b
The new label_scan() function reads a large buffer of data from the start of the disk, and saves it so that multiple structs can be read from it. Previously, only the label_header was read from this buffer, and the code which needed data structures that immediately followed the label_header would read those from disk separately. This created a large number of small, unnecessary disk reads. In each place that the two read paths (label_scan and vg_read) need to read data from disk, first check if that data is already available from the label_read_data buffer, and if so just copy it from the buffer instead of reading from disk. Code changes ------------ - passing the label_read_data struct down through both read paths to make it available. - before every disk read, first check if the location and size of the desired piece of data exists fully in the label_read_data buffer, and if so copy it from there. Otherwise, use the existing code to read the data from disk. - adding some log_error messages on existing error paths that were already being updated for the reasons above. - using similar naming for parallel functions on the two parallel read paths that are being updated above. label_scan path calls: read_metadata_location_summary, text_read_metadata_summary vg_read path calls: read_metadata_location_vg, text_read_metadata_file Previously, those functions were named: label_scan path calls: vgname_from_mda, text_vgsummary_import vg_read path calls: _find_vg_rlocn, text_vg_import_fd I/O changes ----------- In the label_scan path, the following data is either copied from label_read_data or read from disk for each PV: - label_header and pv_header - mda_header (in _raw_read_mda_header) - vg metadata name (in read_metadata_location_summary) - vg metadata (in config_file_read_fd) Total of 4 reads per PV in the label_scan path. In the vg_read path, the following data is either copied from label_read_data or read from disk for each PV: - mda_header (in _raw_read_mda_header) - vg metadata name (in read_metadata_location_vg) - vg metadata (in config_file_read_fd) Total of 3 reads per PV in the vg_read path. For a common read/reporting command, each PV will be: - read by the command's initial lvmcache_label_scan() - read by lvmcache_label_rescan_vg() at the start of vg_read() - read by vg_read() Previously, this would cause 11 synchronous disk reads per PV: 4 from lvmcache_label_scan(), 4 from lvmcache_label_rescan_vg() and 3 from vg_read(). With this commit's optimization, there are now 2 async disk reads per PV: 1 from lvmcache_label_scan() and 1 from lvmcache_label_rescan_vg(). When a second mda is used on a PV, it is located at the end of the PV. This second mda and copy of metadata will not be found in the label_read_data buffer, and will always require separate disk reads.
113 lines
3.3 KiB
C
113 lines
3.3 KiB
C
/*
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* Copyright (C) 2001-2004 Sistina Software, Inc. All rights reserved.
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* Copyright (C) 2004-2006 Red Hat, Inc. All rights reserved.
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*
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* This file is part of LVM2.
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*
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* This copyrighted material is made available to anyone wishing to use,
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* modify, copy, or redistribute it subject to the terms and conditions
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* of the GNU Lesser General Public License v.2.1.
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*
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* You should have received a copy of the GNU Lesser General Public License
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* along with this program; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#ifndef _LVM_TEXT_LAYOUT_H
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#define _LVM_TEXT_LAYOUT_H
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#include "config.h"
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#include "metadata.h"
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#include "lvmcache.h"
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#include "uuid.h"
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/* disk_locn and data_area_list are defined in format-text.h */
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/*
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* PV header extension versions:
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* - version 1: bootloader area support
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* - version 2: PV_EXT_USED flag support
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*/
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#define PV_HEADER_EXTENSION_VSN 2
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struct pv_header_extension {
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uint32_t version;
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uint32_t flags;
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/* NULL-terminated list of bootloader areas */
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struct disk_locn bootloader_areas_xl[0];
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} __attribute__ ((packed));
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/* Fields with the suffix _xl should be xlate'd wherever they appear */
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/* On disk */
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struct pv_header {
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int8_t pv_uuid[ID_LEN];
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/* This size can be overridden if PV belongs to a VG */
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uint64_t device_size_xl; /* Bytes */
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/* NULL-terminated list of data areas followed by */
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/* NULL-terminated list of metadata area headers */
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struct disk_locn disk_areas_xl[0]; /* Two lists */
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} __attribute__ ((packed));
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/*
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* Ignore this raw location. This allows us to
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* ignored metadata areas easily, and thus balance
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* metadata across VGs with many PVs.
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*/
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#define RAW_LOCN_IGNORED 0x00000001
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/* On disk */
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struct raw_locn {
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uint64_t offset; /* Offset in bytes to start sector */
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uint64_t size; /* Bytes */
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uint32_t checksum;
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uint32_t flags;
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} __attribute__ ((packed));
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int rlocn_is_ignored(const struct raw_locn *rlocn);
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void rlocn_set_ignored(struct raw_locn *rlocn, unsigned mda_ignored);
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/* On disk */
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/* Structure size limited to one sector */
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struct mda_header {
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uint32_t checksum_xl; /* Checksum of rest of mda_header */
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int8_t magic[16]; /* To aid scans for metadata */
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uint32_t version;
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uint64_t start; /* Absolute start byte of mda_header */
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uint64_t size; /* Size of metadata area */
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struct raw_locn raw_locns[0]; /* NULL-terminated list */
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} __attribute__ ((packed));
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struct mda_header *raw_read_mda_header(const struct format_type *fmt,
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struct device_area *dev_area,
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struct label_read_data *ld);
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struct mda_lists {
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struct dm_list dirs;
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struct dm_list raws;
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struct metadata_area_ops *file_ops;
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struct metadata_area_ops *raw_ops;
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};
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struct mda_context {
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struct device_area area;
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uint64_t free_sectors;
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struct raw_locn rlocn; /* Store inbetween write and commit */
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};
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/* FIXME Convert this at runtime */
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#define FMTT_MAGIC "\040\114\126\115\062\040\170\133\065\101\045\162\060\116\052\076"
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#define FMTT_VERSION 1
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#define MDA_HEADER_SIZE 512
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#define LVM2_LABEL "LVM2 001"
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#define MDA_SIZE_MIN (8 * (unsigned) lvm_getpagesize())
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int read_metadata_location_summary(const struct format_type *fmt, struct mda_header *mdah,
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struct label_read_data *ld,
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struct device_area *dev_area, struct lvmcache_vgsummary *vgsummary,
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uint64_t *mda_free_sectors);
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#endif
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