On 2020/3/14 上午5:09, Josef Bacik wrote: > In debugging Zygo's huge commit delays I noticed we were burning a bunch of time > doing READA in cases where we don't need to. The way READA works in btrfs is > we'll load up adjacent nodes and leaves as we walk down. This is useful for > operations where we're going to be reading sequentially across the tree. > > But for delayed refs we're looking up one bytenr, and then another one which > could be elsewhere in the tree. With large enough extent trees this results in > a lot of unneeded latency. > > The same applies to build_backref_tree, but that's even worse because we're > looking up backrefs, which are essentially randomly spread out across the extent > root. Thanks, There are quite some other locations abusing READA. E.g. btrfs_read_block_groups(), where we're just searching for block group items. There is no guarantee that next block group item is in next a few leaves. I guess it's a good time to review all READA abuse. Or would you mind me to do that? Thanks, Qu > > Josef >
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