linux-kernel - Re: [PATCH] NFS: allow name_to_handle

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Date:   Wed, 6 Dec 2017 21:34:29 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     NeilBrown <neilb@...e.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Trond Myklebust <trond.myklebust@...marydata.com>,
        Anna Schumaker <Anna.Schumaker@...app.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        lkml <linux-kernel@...r.kernel.org>,
        "linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Lennart Poettering <lennart@...ttering.net>
Subject: Re: [PATCH] NFS: allow name_to_handle_at() to work for Amazon EFS.

On Thu, Dec 07, 2017 at 02:20:05PM +1100, NeilBrown wrote:
> We can allocate in fs/notify/fdinfo.c:show_fdinfo() which is
> the earliest 'notify' specific code to run.  There is no
> opportunity to return an error but GFP_KERNEL allocations under 1 page
> never fail..

"never"

 * The default allocator behavior depends on the request size. We have a concept
 * of so called costly allocations (with order > PAGE_ALLOC_COSTLY_ORDER).
 * !costly allocations are too essential to fail so they are implicitly
 * non-failing by default (with some exceptions like OOM victims might fail so
 * the caller still has to check for failures) while costly requests try to be
 * not disruptive and back off even without invoking the OOM killer.
 * The following three modifiers might be used to override some of these
 * implicit rules