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scan: use up to 1024 max bcache blocks

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Create bcache with one block per device that
will be scanned up to 1024 max blocks.
This commit is contained in:
David Teigland
2018-05-15 12:16:58 -05:00
parent fb0aca86f8
commit 3bbc17a670
1 changed files with 28 additions and 17 deletions
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45
lib/label/label.c
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@ -623,32 +623,46 @@ static int _scan_list(struct cmd_context *cmd, struct dev_filter *f,
return 1;
}
/*
* How many blocks to set up in bcache? Is 1024 a good max?
*
* Currently, we tell bcache to set up N blocks where N
* is the number of devices that are going to be scanned.
* Reasons why this number may not be be a good choice:
*
* - there may be a lot of non-lvm devices, which
* would make this number larger than necessary
*
* - each lvm device may use more than one cache
* block if the metadata is large enough or it
* uses more than one metadata area, which
* would make this number smaller than it
* should be for the best performance.
*
* This is even more tricky to estimate when lvmetad
* is used, because it's hard to predict how many
* devs might need to be scanned when using lvmetad.
* This currently just sets up bcache with MIN blocks.
*/
#define MIN_BCACHE_BLOCKS 32
#define MAX_BCACHE_BLOCKS 1024
static int _setup_bcache(int cache_blocks)
{
struct io_engine *ioe;
/* No devices can happen, just create bcache with any small number. */
if (cache_blocks < MIN_BCACHE_BLOCKS)
cache_blocks = MIN_BCACHE_BLOCKS;
/*
* 100 is arbitrary, it's the max number of concurrent aio's
* possible, i.e, the number of devices that can be read at
* once. Should this be configurable?
*/
if (cache_blocks > MAX_BCACHE_BLOCKS)
cache_blocks = MAX_BCACHE_BLOCKS;
if (!(ioe = create_async_io_engine())) {
log_error("Failed to create bcache io engine.");
return 0;
}
/*
* Configure one cache block for each device on the system.
* We won't generally need to cache that many because some
* of the devs will not be lvm devices, and we don't need
* an entry for those. We might want to change this.
*/
if (!(scan_bcache = bcache_create(BCACHE_BLOCK_SIZE_IN_SECTORS, cache_blocks, ioe))) {
log_error("Failed to create bcache with %d cache blocks.", cache_blocks);
return 0;
@ -708,10 +722,6 @@ int label_scan(struct cmd_context *cmd)
log_debug_devs("Found %d devices to scan", dm_list_size(&all_devs));
if (!scan_bcache) {
/*
* FIXME: there should probably be some max number of
* cache blocks we use when setting up bcache.
*/
if (!_setup_bcache(dm_list_size(&all_devs)))
return 0;
}
@ -939,7 +949,8 @@ out:
* This is only needed when commands are using lvmetad, in which case they
* don't do an initial label_scan, but may later need to rescan certain devs
* from disk and call this function. FIXME: is there some better number to
* choose here?
* choose here? How should we predict the number of devices that might need
* scanning when using lvmetad?
*/
int label_scan_setup_bcache(void)