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labels: avoid metadata area read using async read data

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Copy the metadata out of the initial async read buffer
instead of performing another two synchronous reads
(first to check vgname, second to read all metadata.)
This commit is contained in:
David Teigland
2017-07-27 16:25:14 -05:00
parent 2be6ffca25
commit 4057e092f7
9 changed files with 116 additions and 46 deletions
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53
lib/label/label.c
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@@ -463,13 +463,30 @@ static int _label_read_async_start(struct cmd_context *cmd, io_context_t aio_ctx
iocb->u.c.offset = 0;
ret = io_submit(aio_ctx, 1, &iocb);
if (ret < 0)
/*
* This means that the number of devices exceeded the number of events
* set up in io_setup().
*/
if (ret == -EAGAIN) {
log_debug_devs("Reading label no aio event for %s", dev_name(ld->dev));
return 0;
}
if (ret < 0) {
log_debug_devs("Reading label aio submit error %d for %s", ret, dev_name(ld->dev));
return 0;
}
return 1;
}
#define MAX_GET_EVENTS 8
/*
* We'll collect the results of this many async reads
* in one system call. It shouldn't matter much what
* number is used here.
*/
#define MAX_GET_EVENTS 16
/*
* Reap aio reads from devices.
@@ -555,6 +572,15 @@ static int _label_read_async_process(struct cmd_context *cmd, struct label_read_
return r;
}
/*
* The number of events to use in io_setup(),
* which is the limit on the number of concurrent
* async i/o's we can submit. After all these are
* used, io_submit() returns -EAGAIN, and we revert
* to doing synchronous io.
*/
#define MAX_ASYNC_EVENTS 1024
/*
* label_scan iterates over all visible devices, looking
* for any that belong to lvm, and fills lvmcache with
@@ -593,25 +619,30 @@ int label_scan_async(struct cmd_context *cmd)
*
* This data is meant to big large enough to cover all the
* headers and metadata that need to be read from the device
* during the label scan:
* during the label scan for most common cases.
*
* 1. one of the first four sectors holds:
* label_header, pv_header, pv_header_extention
*
* 2. the mda_header whose location is found from 1,
* (is typically at 4096.)
* 2. the mda_header whose location is found from 1.
*
* 3. the metadata whose location is from found 2,
* (is typically at 16896.)
* 3. the metadata whose location is from found 2.
*
* If during processing, metadata needs to be read in a region
* beyond this buffer, then the code will revert do doing a
* synchronous read of the data it needs.
*/
buf_len = ASYNC_SCAN_SIZE;
/*
* if aio setup fails, caller will revert to sync scan
*/
memset(&aio_ctx, 0, sizeof(io_context_t));
error = io_setup(128, &aio_ctx);
/*
* if aio setup fails, caller will revert to sync scan
* The number of events set up here is the max number of
* concurrent async reads that can be submitted. After
* all of those are used, we revert to synchronous reads.
*/
error = io_setup(MAX_ASYNC_EVENTS, &aio_ctx);
if (error < 0) {
log_debug_devs("async io setup error %d, reverting to sync io.", error);
return_0;