Date: Wed, 28 Nov 2012 00:36:40 +0000 (UTC) From: "Pedro F. Giffuni" <pfg@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r243641 - head/sys/fs/ext2fs Message-ID: <201211280036.qAS0aeSO094520@svn.freebsd.org>
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Author: pfg Date: Wed Nov 28 00:36:40 2012 New Revision: 243641 URL: http://svnweb.freebsd.org/changeset/base/243641 Log: Partially bring r242520 to ext2fs. When a file is first being written, the dynamic block reallocation (implemented by ext2_reallocblks) relocates the file's blocks so as to cluster them together into a contiguous set of blocks on the disk. When the cluster crosses the boundary into the first indirect block, the first indirect block is initially allocated in a position immediately following the last direct block. Block reallocation would usually destroy locality by moving the indirect block out of the way to keep the data blocks contiguous. The issue was diagnosed long ago by Bruce Evans on ffs and surfaced on ext2fs when block reallocaton was ported. This is only a partial solution based on the similarities with FFS. We still require more review of the allocation details that vary in ext2fs. Reported by: bde MFC after: 1 week Modified: head/sys/fs/ext2fs/ext2_alloc.c Modified: head/sys/fs/ext2fs/ext2_alloc.c ============================================================================== --- head/sys/fs/ext2fs/ext2_alloc.c Wed Nov 28 00:02:17 2012 (r243640) +++ head/sys/fs/ext2fs/ext2_alloc.c Wed Nov 28 00:36:40 2012 (r243641) @@ -197,6 +197,18 @@ ext2_reallocblks(ap) panic("ext2_reallocblks: non-cluster"); #endif /* + * If the cluster crosses the boundary for the first indirect + * block, leave space for the indirect block. Indirect blocks + * are initially laid out in a position after the last direct + * block. Block reallocation would usually destroy locality by + * moving the indirect block out of the way to make room for + * data blocks if we didn't compensate here. We should also do + * this for other indirect block boundaries, but it is only + * important for the first one. + */ + if (start_lbn < NDADDR && end_lbn >= NDADDR) + return (ENOSPC); + /* * If the latest allocation is in a new cylinder group, assume that * the filesystem has decided to move and do not force it back to * the previous cylinder group.
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