diff options
author | bde <bde@FreeBSD.org> | 2004-03-13 02:56:27 +0000 |
---|---|---|
committer | bde <bde@FreeBSD.org> | 2004-03-13 02:56:27 +0000 |
commit | 58d250bc297a7b203b5c88431b342a311e3169f0 (patch) | |
tree | 20547bb052b7f44301f236de93038bd16db222b1 | |
parent | d90c60e2d628a89b1bc406a82fbbf86a8e21a747 (diff) | |
download | FreeBSD-src-58d250bc297a7b203b5c88431b342a311e3169f0.zip FreeBSD-src-58d250bc297a7b203b5c88431b342a311e3169f0.tar.gz |
Align the offset in vn_rdwr_inchunks() so that at most the first and
the last chunk are misaligned relative to a MAXBSIZE byte boundary.
vn_rdwr_inchunks() is used mainly for elf core dumps, and elf sections
are usually perfectly misaligned relative to MAXBSIZE, and chunking
prevents the file system from doing much realigning.
This gives a surprisingly large speedup for core dumps -- from 50 to
13 seconds for a 512MB core dump here. The pessimization was mostly
from an interaction of the misalignment with IO_DIRECT. It increased
the number of i/o's for each chunk by a factor of 5 (3 writes and 2
read-before-writes instead of 1 write).
-rw-r--r-- | sys/kern/vfs_vnops.c | 12 |
1 files changed, 11 insertions, 1 deletions
diff --git a/sys/kern/vfs_vnops.c b/sys/kern/vfs_vnops.c index aa49d6f..e67e22e 100644 --- a/sys/kern/vfs_vnops.c +++ b/sys/kern/vfs_vnops.c @@ -476,8 +476,18 @@ vn_rdwr_inchunks(rw, vp, base, len, offset, segflg, ioflg, active_cred, int error = 0; do { - int chunk = (len > MAXBSIZE) ? MAXBSIZE : len; + int chunk; + /* + * Force `offset' to a multiple of MAXBSIZE except possibly + * for the first chunk, so that filesystems only need to + * write full blocks except possibly for the first and last + * chunks. + */ + chunk = MAXBSIZE - (uoff_t)offset % MAXBSIZE; + + if (chunk > len) + chunk = len; if (rw != UIO_READ && vp->v_type == VREG) bwillwrite(); error = vn_rdwr(rw, vp, base, chunk, offset, segflg, |