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Message-ID: <1307022e77a0853de8c417ff43128908@josephdwagner.info> Date: Mon, 03 Jun 2013 09:12:09 -0700 From: "Joseph D. Wagner" <joe@...ephdwagner.info> To: <linux-ext4@...r.kernel.org> Subject: RFC: [Bug 968876] e4defrag incorrectly calculates optimum extents https://bugzilla.redhat.com/show_bug.cgi?id=968876 The "Total/best extents" calculation for done in the e4defrag program doesn't seems to not consider the limit of 32768 file system blocks (see /usr/src/linux/fs/ext4/ext4_extents.h comment EXT_INIT_MAX_LEN) in an extent when computing the "best" value. It seems to presume 2G is the best extent size, but on a file system with a 4kb block size the largest available extent is 128M not 2G. (The best extent size calculation in e4defrag seems to be based on block group size but the underlying implementation in the kernel is limited to a __le16 blocks and uses up one whole bit of that to flag whether the extent is initialized, which actually produces a one-block perturbation in the actual limit based on how the extent was allocated (e.g. whether falloc used FS_KEEP_SIZE or not), go go gadget perturbed math. 8-)). Example: -rw-r--r-- 1 rwhite rwhite 5.0G Jun 13 16:28 CentOS.qcow2 yeilds output: (where "/3" is wrong). Total/best extents 152/3 Proposed patch available here: http://pastebin.com/9XTFcVM0 Joseph D. Wagner -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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