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bigalloc

bigalloc

Posted Nov 30, 2011 21:16 UTC (Wed) by walex (subscriber, #69836)
In reply to: bigalloc by iabervon
Parent article: Improving ext4: bigalloc, inline data, and metadata checksums

Note that 'ext4' supports extents, so files can get allocated with very large contiguous extents already, for example for a 70MB file:

#  du -sm /usr/share/icons/oxygen/icon-theme.cache
69      /usr/share/icons/oxygen/icon-theme.cache
#  filefrag /usr/share/icons/oxygen/icon-theme.cache
/usr/share/icons/oxygen/icon-theme.cache: 1 extent found
#  df -T /usr/share/icons/oxygen/icon-theme.cache
Filesystem    Type   1M-blocks      Used Available Use% Mounted on
/dev/sda3     ext4       25383     12558     11545  53% /

But so far the free space has been tracked in block-sized units, and the new thing seems to change the amount of free space accounted for by each bit in the free space bitmap.

Which means that as surmised the granularity of allocation has changed (for example minimum extent size).


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