• Andreas Gruenbacher's avatar
    mbcache: add reusable flag to cache entries · 6048c64b
    Andreas Gruenbacher authored
    To reduce amount of damage caused by single bad block, we limit number
    of inodes sharing an xattr block to 1024. Thus there can be more xattr
    blocks with the same contents when there are lots of files with the same
    extended attributes. These xattr blocks naturally result in hash
    collisions and can form long hash chains and we unnecessarily check each
    such block only to find out we cannot use it because it is already
    shared by too many inodes.
    
    Add a reusable flag to cache entries which is cleared when a cache entry
    has reached its maximum refcount.  Cache entries which are not marked
    reusable are skipped by mb_cache_entry_find_{first,next}. This
    significantly speeds up mbcache when there are many same xattr blocks.
    For example for xattr-bench with 5 values and each process handling
    20000 files, the run for 64 processes is 25x faster with this patch.
    Even for 8 processes the speedup is almost 3x. We have also verified
    that for situations where there is only one xattr block of each kind,
    the patch doesn't have a measurable cost.
    
    [JK: Remove handling of setting the same value since it is not needed
    anymore, check for races in e_reusable setting, improve changelog,
    add measurements]
    Signed-off-by: 's avatarAndreas Gruenbacher <agruenba@redhat.com>
    Signed-off-by: 's avatarJan Kara <jack@suse.cz>
    Signed-off-by: 's avatarTheodore Ts'o <tytso@mit.edu>
    6048c64b
mbcache.h 1.57 KB