> you may use "#mount /dev/sda1 /mnt/tmp -o fsync=10" which means "fsync
> once when invoked fsync 10 times"
or if 5 (may be use sys.vm.dirty_writeback_centisecs) seconds have elapsed since last fsync.
-devsk
----- Original Message ----
From: Xu CanHao <xucanhao@xxxxxxxxx>
To: reiserfs-devel@xxxxxxxxxxxxxxx
Sent: Thursday, June 7, 2007 5:14:46 AM
Subject: Reiser4 performance bottlenecks and possible solutions
Hello!
Since performance is one of the most important aspect of Reiser4, I
indeed encountered some performance bottlenecks of Reiser4 during my
daily usage. The following is my own(possibly wrong) experiences:
1, Tail-conversion/Extent-only
May save space at a 5-10 percent, while impacts performance much more
greater. Extent-only performs better.
2, read()...
Old read_unix_file() is not efficient, especially in
read_unix_file_container_tails(). So I think generic_file_read() is
better for Extent-only users.
1+2, Extent-only + generic_file_read()
During my benchmark, 1+2 provides 10%-400% better performance(varies
with the benchmark utility)
3, fsync()
Terrible fsync() performance has been talked for a thousand times
without a full solution. I'm thinking of a temporary solution: adding
a mount option and let the user determine the fsync() frequency(yes,
you may lose data when power-fail), things like:
int sync_unix_file(struct file *file, struct dentry *dentry, int datasync)
{
reiser4_context *ctx;
txn_atom *atom;
reiser4_block_nr reserve;
reiser4_super_info_data *sbinfo;
ctx = init_context(dentry->d_inode->i_sb);
if (IS_ERR(ctx))
return PTR_ERR(ctx);
sbinfo = get_current_super_private();
if (sbinfo->fsync == 0)
{
reiser4_exit_context(ctx);
return 0;
}
else if (sbinfo->fsync == 1)
{
fsync_file: reserve = estimate_update_common(dentry->d_inode);
if (reiser4_grab_space(reserve, BA_CAN_COMMIT)) {
reiser4_exit_context(ctx);
return RETERR(-ENOSPC);
}
write_sd_by_inode_common(dentry->d_inode);
atom = get_current_atom_locked();
spin_lock_txnh(ctx->trans);
force_commit_atom(ctx->trans);
reiser4_exit_context(ctx);
return 0;
}
else if (sbinfo->fsync > 1)
{
fsync_num++;
if (fsync_num >= sbinfo->fsync) {
fsync_num = 0;
goto fsync_file;
}
reiser4_exit_context(ctx);
return 0;
}
return 0;
}
you may use "#mount /dev/sda1 /mnt/tmp -o fsync=10" which means "fsync
once when invoked fsync 10 times"
4, Relocation/Overwrite
Should you take 1+2 the default value 64 of flush.relocate_threshold
and flush.relocate_distance may not suitable, a lower value maybe
better for most case.
1+2+3+4
If you take all of them, the performance gain would be dramatically
and still as stable as before, at least for my months of experience.
Thanks!
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