linux-ext4 - Re: [PATCH 2/7] mm: Protect operations adding pages to page cache with i_mapping

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Date:   Thu, 15 Apr 2021 15:11:59 +0200
From:   Jan Kara <jack@...e.cz>
To:     Dave Chinner <david@...morbit.com>
Cc:     Jan Kara <jack@...e.cz>, linux-fsdevel@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        Ted Tso <tytso@....edu>, Christoph Hellwig <hch@...radead.org>,
        Amir Goldstein <amir73il@...il.com>
Subject: Re: [PATCH 2/7] mm: Protect operations adding pages to page cache
 with i_mapping_lock

On Thu 15-04-21 07:57:39, Dave Chinner wrote:
> On Wed, Apr 14, 2021 at 02:23:19PM +0200, Jan Kara wrote:
> > Regarding the name: How about i_pages_rwsem? The lock is protecting
> > invalidation of mapping->i_pages and needs to be held until insertion of
> > pages into i_pages is safe again...
> 
> I don't actually have a good name for this right now. :(
> 
> The i_pages structure has it's own internal locking, so
> i_pages_rwsem implies things that aren't necessarily true, and
> taking a read lock for insertion for something that is named like a
> structure protection lock creates cognitive dissonance...
> 
> I keep wanting to say "lock for invalidation" and "lock to exclude
> invalidation" because those are the two actions that we need for
> coherency of operations. But they are way too verbose for an actual
> API...
> 
> So I want to call this an "invalidation lock" of some kind (no need
> to encode the type in the name!), but haven't worked out a good
> shorthand for "address space invalidation coherency mechanism"...

So "invalidate_lock" was just next on my list of things to suggest so I'm
fine with that name. Or maybe block_invalidate_lock, block_remove_lock,
map_remove_lock, ... Dunno :).

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR