On 11/30/06, Wendy Cheng <wcheng@xxxxxxxxxx> wrote:
How about a simple and plain change with this uploaded patch .... The idea is, instead of unconditionally dropping every buffer associated with the particular mount point (that defeats the purpose of page caching), base kernel exports the "drop_pagecache_sb()" call that allows page cache to be trimmed. More importantly, it is changed to offer the choice of not randomly purging any buffer but the ones that seem to be unused (i_state is NULL and i_count is zero). This will encourage filesystem(s) to pro actively response to vm memory shortage if they choose so. From our end (cluster locks are expensive - that's why we cache them), one of our kernel daemons will invoke this newly exported call based on a set of pre-defined tunables. It is then followed by a lock reclaim logic to trim the locks by checking the page cache associated with the inode (that this cluster lock is created for). If nothing is attached to the inode (based on i_mapping->nrpages count), we know it is a good candidate for trimming and will subsequently drop this lock (instead of waiting until the end of vfs inode life cycle).
I have a patch that is a more comprehensive version of this idea, but it is not fully debugged, and has suffered some bitrot in the past couple months. This turns out to be a good performance improvement in the general case too, but is more complex than your idea because there are real locking changes needed to avoid deadlocks. I can send you a copy of the patch if you are interested.
Note that I could do invalidate_inode_pages() within our kernel modules to accomplish what drop_pagecache_sb() does (without coming here to bug people) but I don't have access to inode_lock as an external kernel module. So either EXPORT_SYMBOL(inode_lock) or this patch ?
like i said above, you have to be careful when touching inode_lock, dcache_lock, and the mapping's tree_lock, because of potential deadlocks. the mapping's lock can be taken from softirq context, but the inode and dcache locks cannot. NATE - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
