linux-ext4 - Re: Locality of extent status tree traversal

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Message-ID: <CALe4XzZxzMaDACmrVHJZ6ronWMd9JC+1t6EetYUu39FitofqDg@mail.gmail.com>
Date:   Tue, 7 May 2019 13:56:27 -0500
From:   Probir Roy <proy.cse@...il.com>
To:     "Theodore Ts'o" <tytso@....edu>
Cc:     linux-ext4@...r.kernel.org
Subject: Re: Locality of extent status tree traversal

> block number (e.g., the location on disk).  It's a cache; lookups are
> fast, and is an in-memory lookup.  Well, it's a little more than a
> cache, it also stores some information for delayed allocation buffered
> writes.

For sequential access, it will traverse almost the same path of the
tree. How deep the extent status tree be in general? If the tree is
much deeper, the sequential accesses would have many repeated nodes
traversal on the tree for the lookup. Have you observed significant
bottleneck on "ext4_es_lookup_extent"? Can it be removed by caching
the parent node?

-- 
Probir Roy