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Date:   Wed, 29 Jan 2020 17:15:46 -0500
From:   "Theodore Y. Ts'o" <>
To:     Konstantin Khlebnikov <>
Cc:, David Howells <>,
        Alexander Viro <>,,,
        Dmitry Monakhov <>
Subject: Re: [PATCH RFC] ext4: skip concurrent inode updates in lazytime

On Wed, Jan 29, 2020 at 06:44:05PM +0300, Konstantin Khlebnikov wrote:
> Function ext4_update_other_inodes_time() implements optimization which
> opportunistically updates times for inodes within same inode table block.
> For now	concurrent inode lookup by number does not scale well because
> inode hash table is protected with single spinlock. It could become very
> hot at concurrent writes to fast nvme when inode cache has enough inodes.
> Probably someday inode hash will become searchable under RCU.
> (see linked patchset by David Howells)
> Let's skip concurrent updates instead of wasting cpu time at spinlock.
> Signed-off-by: Konstantin Khlebnikov <>
> Link:

Hmm.... I wonder what Al thinks of adding a varaint of
find_inode_nowait() which uses tries to grab the inode_hash_lock()
using a trylock, and returns ERR_PTR(-EAGAIN) if the attempt to grab
the lock fails.

This might be better since it will prevent other conflicts between
ext4_update_other_inodes_time() and other attempts to lookup inodes
which can't be skipped if things are busy.

      	       	       	  	     - Ted

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