linux-kernel - Re: [PATCH] mm: fix page cache convergence regression

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Message-ID: <CAHk-=wjcO7WjWyAoBmXDWcn7spfJbbgF_tXaHrqANVqEH8DGmQ@mail.gmail.com>
Date:   Tue, 25 Jun 2019 05:52:00 +0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux-MM <linux-mm@...ck.org>, Cgroups <cgroups@...r.kernel.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        kernel-team@...com
Subject: Re: [PATCH] mm: fix page cache convergence regression

On Mon, Jun 24, 2019 at 11:19 PM Johannes Weiner <hannes@...xchg.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