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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.
128 lines
3.3 KiB
C
128 lines
3.3 KiB
C
/*
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* Copyright (C) 2002-2004 Sistina Software, Inc. All rights reserved.
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* Copyright (C) 2004-2007 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_LABEL_H
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#define _LVM_LABEL_H
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#include "uuid.h"
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#include "device.h"
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#include "toolcontext.h"
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#define LABEL_ID "LABELONE"
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#define LABEL_SIZE SECTOR_SIZE /* Think very carefully before changing this */
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#define LABEL_SCAN_SECTORS 4L
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#define LABEL_SCAN_SIZE (LABEL_SCAN_SECTORS << SECTOR_SHIFT)
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struct labeller;
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void allow_reads_with_lvmetad(void);
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struct label_read_data {
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struct dev_async_io *aio;
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char *buf; /* points to aio->buf */
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struct device *dev;
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struct dm_list list;
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int buf_len; /* same as aio->buf_len */
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int result; /* same as aio->result */
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int try_sync;
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int process_done;
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};
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/* On disk - 32 bytes */
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struct label_header {
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int8_t id[8]; /* LABELONE */
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uint64_t sector_xl; /* Sector number of this label */
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uint32_t crc_xl; /* From next field to end of sector */
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uint32_t offset_xl; /* Offset from start of struct to contents */
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int8_t type[8]; /* LVM2 001 */
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} __attribute__ ((packed));
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/* In core */
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struct label {
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char type[8];
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uint64_t sector;
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struct labeller *labeller;
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struct device *dev;
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void *info;
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};
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struct labeller;
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struct label_ops {
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/*
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* Is the device labelled with this format ?
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*/
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int (*can_handle) (struct labeller * l, void *buf, uint64_t sector);
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/*
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* Write a label to a volume.
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*/
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int (*write) (struct label * label, void *buf);
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/*
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* Read a label from a volume.
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*/
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int (*read) (struct labeller * l, struct device * dev,
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void *label_buf,
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struct label_read_data *ld, struct label ** label);
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/*
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* Additional consistency checks for the paranoid.
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*/
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int (*verify) (struct labeller * l, void *buf, uint64_t sector);
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/*
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* Populate label_type etc.
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*/
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int (*initialise_label) (struct labeller * l, struct label * label);
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/*
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* Destroy a previously read label.
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*/
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void (*destroy_label) (struct labeller * l, struct label * label);
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/*
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* Destructor.
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*/
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void (*destroy) (struct labeller * l);
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};
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struct labeller {
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struct label_ops *ops;
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const struct format_type *fmt;
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};
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int label_init(void);
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void label_exit(void);
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int label_register_handler(struct labeller *handler);
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struct labeller *label_get_handler(const char *name);
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int label_remove(struct device *dev);
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int label_read(struct device *dev, struct label **label, uint64_t scan_sector);
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int label_write(struct device *dev, struct label *label);
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int label_verify(struct device *dev);
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struct label *label_create(struct labeller *labeller);
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void label_destroy(struct label *label);
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int label_scan_force(struct cmd_context *cmd);
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int label_scan(struct cmd_context *cmd);
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int label_scan_devs(struct cmd_context *cmd, struct dm_list *devs);
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struct label_read_data *get_label_read_data(struct cmd_context *cmd, struct device *dev);
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void label_scan_destroy(struct cmd_context *cmd);
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#endif
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