On Mon, 03 Oct 2011 12:00:00 -0700, Allison Henderson <achender@xxxxxxxxxxxxxxxxxx> wrote: > Hi all, > > I've been working on locating all the existing uses of i_mutex in the > current ext4 code because I know we are planning to reduce the usage of > i_mutex in ext4. So I've gone through the ext4 code and also the vfs > code and come up with a list of ext4 items that appear to be protected > under i_mutex. I'm thinking about doing a patch to replace i_mutex with > a private ext4 mutex, and I wanted to update folks on this idea and pick > up any feed back people might have. > > I'm thinking maybe we can have a separate mutex for functions that only > modify meta data like ext4_ioctl and ext4_setattr to help relieve > unneeded contention. Are you going to change vfs core locking? > And then the rest of functions that are modifying > data can go under a data mutex (including truncate since sometimes > ext4_ioctl and ext4_setattr will call ext4_truncate if they modify i_size). > > So these are ext4 functions that currently lock i_mutex: > > ext4_sync_file > ext4_fallocate > ext4_move_extents via two helper routines: > mext_inode_double_lock and mext_inode_double_unlock > ext4_ioctl (for the EXT4_IOC_SETFLAGS ioctl) > ext4_quota_write We can easily avoid i_mutex on quota write because quota file can not be truncated, and grows only in case of new dquot added. I'll send you a patch. > ext4_llseek > ext4_end_io_work > ext4_evict_inode (only while calling ext4_flush_completed_IO) > ext4_ind_direct_IO (only while calling ext4_flush_completed_IO) > > > And these are ext4 functions that have i_mutex locked by the vfs layer. > So we will need to lock the new private mutex here too if we want them > to be synchronous with the above functions. > > ext4_setattr > ext4_da_writepages > ext4_rmdir > ext4_unlink > ext4_symlink > ext4_link > ext4_rename > > And one unique case: > ext4_fiemap calls generic_block_fiemap and passes it a function pointer > to ext4_get_block. generic_block_fiemap will lock i_mutex before > calling the pointer. I dont think ext4_get_block needs i_mutex locked > all the time, so I think we can just make a wrapper for ext4_get_block > that locks the new private mutex and then we can pass a pointer to the > wrapper. > > > That's my list so far, if anyone knows of one I missed please let me > know, and also if you spot any other places where we can reduce unneeded > contention by using a separate lock. Thx! > > Allison Henderson > -- > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
