linux-kernel - Re: [PATCH v2] mm: shmem: implement POSIX_FADV

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Message-ID: <04ca54ad-0e03-84b1-bf5c-131a582137d4@codeaurora.org>
Date:   Fri, 3 Dec 2021 17:25:40 +0530
From:   Charan Teja Kalla <charante@...eaurora.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Charan Teja Reddy <quic_charante@...cinc.com>, hughd@...gle.com,
        akpm@...ux-foundation.org, vbabka@...e.cz, rientjes@...gle.com,
        david@...hat.com, mhocko@...e.com, surenb@...gle.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm: shmem: implement POSIX_FADV_[WILL|DONT]NEED for
 shmem

()

On 12/2/2021 9:24 PM, Matthew Wilcox wrote:
> Would this change to the documentation have prevented you from making
> this mistake?
> 
>  The advanced API is based around the xa_state.  This is an opaque data
>  structure which you declare on the stack using the XA_STATE()
>  macro.  This macro initialises the xa_state ready to start walking
>  around the XArray.  It is used as a cursor to maintain the position
>  in the XArray and let you compose various operations together without
> -having to restart from the top every time.
> +having to restart from the top every time.  The contents of the xa_state
> +are protected by the rcu_read_lock() or the xas_lock().  If you need to
> +drop whichever of those locks is protecting your state and tree, you must
> +call xas_pause() so that future calls do not rely on the parts of the
> +state which were left unprotected.

Yes, this looks much clear to me.

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