Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <20190524153148.18481-1-hannes@cmpxchg.org> <20190524160417.GB1075@bombadil.infradead.org>
 <20190524173900.GA11702@cmpxchg.org> <20190530161548.GA8415@cmpxchg.org>
 <20190530171356.GA19630@bombadil.infradead.org> <20190624151923.GA10572@cmpxchg.org>
In-Reply-To: <20190624151923.GA10572@cmpxchg.org>
From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Tue, 25 Jun 2019 05:52:00 +0800
Message-ID: <CAHk-=wjcO7WjWyAoBmXDWcn7spfJbbgF_tXaHrqANVqEH8DGmQ@mail.gmail.com>
Subject: Re: [PATCH] mm: fix page cache convergence regression
To:     Johannes Weiner <hannes@cmpxchg.org>
Cc:     Matthew Wilcox <willy@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux-MM <linux-mm@kvack.org>, Cgroups <cgroups@vger.kernel.org>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        kernel-team@fb.com
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Mon, Jun 24, 2019 at 11:19 PM Johannes Weiner <hannes@cmpxchg.org> wrote:
>
> Hey, it's three weeks later and we're about to miss 5.2.
>
> This sucks, Matthew.

Yes.

And I do think that having a real gfp field there would be better than
the very odd xa_flags that is *marked* as being gfp_t, but isn't
really a gfp_t at all.

So how about we apply Johannes' patch, and then work on making that
xa_flags field be a proper type of its own. Because it really isn't a
gfp_t, and never has been, even if there might be some very limited
and hacky overlap right now.

Alternatrively, the subset of bits that _can_ be used as a gfp should
actually be used as such, in xas_alloc/xas_nomem. So that you can do

    xa_init_flags(&mapping->i_pages, XA_FLAGS_LOCK_IRQ | __GFP_ACCOUNT);

in __address_space_init_once() and it would do what it is supposed to do.

Willy?

               Linus