* [RFC] log mode COW
@ 2010-05-11 8:23 Yan, Zheng
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From: Yan, Zheng @ 2010-05-11 8:23 UTC (permalink / raw)
To: linux-btrfs; +Cc: Chris Mason
The aim of log mode COW is solve extent tree performance issue when
free metadata space are scarce and fragmented. The basic idea is:
when cowing a non-shared block, we insert a log entry that maps
the new block to the old block into a special log tree, and do not
update the extent tree. After transaction is fully committed, copy
the new block back to the old location.
Log mode COW can be enabled/disabled by log_mode=%d mount option.
'0' means disable log mode COW; '1' means enable log for tree blocks
that are not reference counted; '2' means enable log for all tree
blocks are not shared.
NOTE: The patch series base on current btrfs-unstable. They are for
test and review only. Enable log mode COW changes disk format.
Regards
Yan, Zheng
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