linux-kernel - Re: [PATCH v5 03/78] xarray: Add the xa_lock to the radix_tree

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Date:   Tue, 26 Dec 2017 19:43:40 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     linux-kernel@...r.kernel.org,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        David Howells <dhowells@...hat.com>,
        Shaohua Li <shli@...nel.org>, Jens Axboe <axboe@...nel.dk>,
        Rehas Sachdeva <aquannie@...il.com>,
        Marc Zyngier <marc.zyngier@....com>, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-nilfs@...r.kernel.org, linux-btrfs@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-raid@...r.kernel.org
Subject: Re: [PATCH v5 03/78] xarray: Add the xa_lock to the radix_tree_root

On Tue, Dec 26, 2017 at 07:54:40PM +0300, Kirill A. Shutemov wrote:
> On Fri, Dec 15, 2017 at 02:03:35PM -0800, Matthew Wilcox wrote:
> > From: Matthew Wilcox <mawilcox@...rosoft.com>
> > 
> > This results in no change in structure size on 64-bit x86 as it fits in
> > the padding between the gfp_t and the void *.
> 
> The patch does more than described in the subject and commit message. At first
> I was confused why do you need to touch idr here. It took few minutes to figure
> it out.
> 
> Could you please add more into commit message about lockname and xa_ locking
> interface since you introduce it here?

Sure!  How's this?

    xarray: Add the xa_lock to the radix_tree_root
    
    This results in no change in structure size on 64-bit x86 as it fits in
    the padding between the gfp_t and the void *.
    
    Initialising the spinlock requires a name for the benefit of lockdep,
    so RADIX_TREE_INIT() now needs to know the name of the radix tree it's
    initialising, and so do IDR_INIT() and IDA_INIT().
    
    Also add the xa_lock() and xa_unlock() family of wrappers to make it
    easier to use the lock.  If we could rely on -fplan9-extensions in
    the compiler, we could avoid all of this syntactic sugar, but that
    wasn't added until gcc 4.6.