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    SubjectRe: [PATCH] prune_icache_sb
    On 11/30/06, Wendy Cheng <> 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.

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      Last update: 2006-11-30 20:35    [W:0.021 / U:2.024 seconds]
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