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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu, 16 Dec 2021 08:31:19 -0800
Message-ID: <CAHk-=wi0H5vmka1_iWe0+Yc6bwtgWn_bEEHCMYsPHYtNJKZHCQ@mail.gmail.com>
Subject: Re: [PATCH v3 56/68] afs: Handle len being extending over page end in write_begin/write_end
To:     David Howells <dhowells@redhat.com>
Cc:     linux-cachefs@redhat.com,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Jeff Layton <jlayton@kernel.org>,
        Marc Dionne <marc.dionne@auristor.com>,
        linux-afs@lists.infradead.org,
        Trond Myklebust <trondmy@hammerspace.com>,
        Anna Schumaker <anna.schumaker@netapp.com>,
        Steve French <sfrench@samba.org>,
        Dominique Martinet <asmadeus@codewreck.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Omar Sandoval <osandov@osandov.com>,
        JeffleXu <jefflexu@linux.alibaba.com>,
        "open list:NFS, SUNRPC, AND..." <linux-nfs@vger.kernel.org>,
        CIFS <linux-cifs@vger.kernel.org>, ceph-devel@vger.kernel.org,
        v9fs-developer@lists.sourceforge.net,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Thu, Dec 16, 2021 at 8:22 AM David Howells <dhowells@redhat.com> wrote:
>
> With transparent huge pages, in the future, write_begin() and write_end()
> may be passed a length parameter that, in combination with the offset into
> the page, exceeds the length of that page.  This allows
> grab_cache_page_write_begin() to better choose the size of THP to allocate.

I still think this is a fundamental bug in the caller. That
"explanation" is weak, and the whole concept smells like week-old fish
to me.

         Linus