[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <ZLVpjhAvk/nAquiY@casper.infradead.org>
Date: Mon, 17 Jul 2023 17:17:18 +0100
From: Matthew Wilcox <willy@...radead.org>
To: David Hildenbrand <david@...hat.com>
Cc: Ryan Roberts <ryan.roberts@....com>,
Andrew Morton <akpm@...ux-foundation.org>,
Yin Fengwei <fengwei.yin@...el.com>,
Yu Zhao <yuzhao@...gle.com>, Yang Shi <shy828301@...il.com>,
"Huang, Ying" <ying.huang@...el.com>, Zi Yan <ziy@...dia.com>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v1 1/3] mm: Allow deferred splitting of arbitrary large
anon folios
On Mon, Jul 17, 2023 at 04:54:58PM +0100, Matthew Wilcox wrote:
> Those are page->flags and page->compound_head for the third page in
> the folio. They don't really need a name; nothing refers to them,
> but it's important that space not be reused ;-)
>
> This is slightly different from _flags_1; we do have some flags which
> reuse the bits (they're labelled as PF_SECOND). Right now, it's only
> PG_has_hwpoisoned, but we used to have PG_double_map. Others may arise.
Sorry, this was incomplete. We do still have per-page flags! HWPoison
is the obvious one, but PG_head is per-page (... think about it ...)
PG_anon_exclusive is actually per-page.
Most of the flags labelled as PF_ANY are mislabelled. PG_private and
PG_private2 are never set/cleared/tested on tail pages. PG_young and
PG_idle are only ever tested on the head page, but some code incorrectly
sets them on tail pages, where those bits are ignored. I tried to fix
that a while ago, but the patch was overlooked and I couldn't be bothered
to try all that hard. I have no clue about PG_vmemmap_self_hosted.
I think PG_isolated is probably never set on compound pages.
PG_owner_priv_1 is a disaster, as you might expect.
Powered by blists - more mailing lists