From: Matthew Wilcox <willy@infradead.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v4 08/25] mm: Handle per-folio private data
Date: Thu, 18 Mar 2021 17:57:51 +0000 [thread overview]
Message-ID: <20210318175751.GS3420@casper.infradead.org> (raw)
In-Reply-To: <YFI6YOe2uU/n2vR6@infradead.org>
On Wed, Mar 17, 2021 at 06:20:32PM +0100, Christoph Hellwig wrote:
> > +static inline void attach_page_private(struct page *page, void *data)
> > +{
> > + attach_folio_private((struct folio *)page, data);
> > +}
> > +
> > +static inline void *detach_page_private(struct page *page)
> > +{
> > + return detach_folio_private((struct folio *)page);
> > +}
>
> I hate these open code casts. Can't we have a single central
> page_to_folio helper, which could also grow a debug check (maybe
> under a new config option) to check that it really is called on a
> head page?
Some of that is already there. We have page_folio() which is the
page_to_folio() helper you're asking for. And folio_flags() (which is
called *all the time*) contains
VM_BUG_ON_PGFLAGS(PageTail(page), page);
Someone passing around a tail pointer cast to a folio is not going to
get very far, assuming CONFIG_DEBUG_VM_PGFLAGS is enabled (most distros
don't, but I do when I'm testing anything THPish).
These helpers aren't going to live for very long ... I expect to have
all filesystems which use attach/detach page private converted to folios
pretty soon. Certainly before any of them _use_ multi-page folios.
Anyway, the simple thing to do is just to use page_folio() here and eat
the cost of calling compound_head() on something we're certain is an
order-0 page. It only defers the win of removing the compound_head()
call; it doesn't preclude it. And it means we're not setting a bad
example here (there really shouldn't be any casts from pages to folios,
except in the folio allocator, which uses the page allocator and then
casts what _must be_ a non-tail page to a folio).
next prev parent reply other threads:[~2021-03-18 17:58 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-05 4:18 [PATCH v4 00/25] Page folios Matthew Wilcox (Oracle)
2021-03-05 4:18 ` [PATCH v4 01/25] mm: Introduce struct folio Matthew Wilcox (Oracle)
2021-03-13 20:37 ` Andrew Morton
2021-03-14 4:07 ` Matthew Wilcox
2021-03-17 17:14 ` Christoph Hellwig
2021-03-18 23:56 ` Balbir Singh
2021-03-19 1:25 ` Matthew Wilcox
2021-03-20 2:09 ` Balbir Singh
2021-03-22 2:52 ` Nicholas Piggin
2021-03-22 3:54 ` Matthew Wilcox
2021-03-05 4:18 ` [PATCH v4 02/25] mm: Add folio_pgdat and folio_zone Matthew Wilcox (Oracle)
2021-03-05 4:18 ` [PATCH v4 03/25] mm/vmstat: Add functions to account folio statistics Matthew Wilcox (Oracle)
2021-03-13 20:37 ` Andrew Morton
2021-03-14 4:11 ` Matthew Wilcox
2021-03-14 4:51 ` Andrew Morton
2021-03-17 17:16 ` Christoph Hellwig
2021-03-05 4:18 ` [PATCH v4 04/25] mm/debug: Add VM_BUG_ON_FOLIO and VM_WARN_ON_ONCE_FOLIO Matthew Wilcox (Oracle)
2021-03-05 4:18 ` [PATCH v4 05/25] mm: Add put_folio Matthew Wilcox (Oracle)
2021-03-05 4:18 ` [PATCH v4 06/25] mm: Add get_folio Matthew Wilcox (Oracle)
2021-03-05 4:18 ` [PATCH v4 07/25] mm: Create FolioFlags Matthew Wilcox (Oracle)
2021-03-15 2:24 ` Matthew Wilcox
2021-03-05 4:18 ` [PATCH v4 08/25] mm: Handle per-folio private data Matthew Wilcox (Oracle)
2021-03-17 17:20 ` Christoph Hellwig
2021-03-18 17:57 ` Matthew Wilcox [this message]
2021-03-05 4:18 ` [PATCH v4 09/25] mm: Add folio_index, folio_page and folio_contains Matthew Wilcox (Oracle)
2021-03-13 20:37 ` Andrew Morton
2021-03-14 3:45 ` Matthew Wilcox
2021-03-17 17:22 ` Christoph Hellwig
2021-03-05 4:18 ` [PATCH v4 10/25] mm/util: Add folio_mapping and folio_file_mapping Matthew Wilcox (Oracle)
2021-03-17 17:26 ` Christoph Hellwig
2021-03-05 4:18 ` [PATCH v4 11/25] mm/memcg: Add folio wrappers for various memcontrol functions Matthew Wilcox (Oracle)
2021-03-05 4:18 ` [PATCH v4 12/25] mm/filemap: Add unlock_folio Matthew Wilcox (Oracle)
2021-03-05 4:18 ` [PATCH v4 13/25] mm/filemap: Add lock_folio Matthew Wilcox (Oracle)
2021-03-05 4:18 ` [PATCH v4 14/25] mm/filemap: Add lock_folio_killable Matthew Wilcox (Oracle)
2021-03-05 4:18 ` [PATCH v4 15/25] mm/filemap: Convert lock_page_async to lock_folio_async Matthew Wilcox (Oracle)
2021-03-17 17:29 ` Christoph Hellwig
2021-03-05 4:18 ` [PATCH v4 16/25] mm/filemap: Convert end_page_writeback to end_folio_writeback Matthew Wilcox (Oracle)
2021-03-05 4:18 ` [PATCH v4 17/25] mm/filemap: Add wait_on_folio_locked & wait_on_folio_locked_killable Matthew Wilcox (Oracle)
2021-03-05 4:18 ` [PATCH v4 18/25] mm/page-writeback: Add wait_on_folio_writeback Matthew Wilcox (Oracle)
2021-03-05 4:18 ` [PATCH v4 19/25] mm/page-writeback: Add wait_for_stable_folio Matthew Wilcox (Oracle)
2021-03-05 4:18 ` [PATCH v4 20/25] mm/filemap: Convert wait_on_page_bit to wait_on_folio_bit Matthew Wilcox (Oracle)
2021-03-17 17:39 ` Christoph Hellwig
2021-03-05 4:18 ` [PATCH v4 21/25] mm/filemap: Add __lock_folio_or_retry Matthew Wilcox (Oracle)
2021-03-05 4:18 ` [PATCH v4 22/25] mm/filemap: Convert wake_up_page_bit to wake_up_folio_bit Matthew Wilcox (Oracle)
2021-03-05 4:18 ` [PATCH v4 23/25] mm/page-writeback: Convert test_clear_page_writeback to take a folio Matthew Wilcox (Oracle)
2021-03-05 4:19 ` [PATCH v4 24/25] mm/filemap: Convert page wait queues to be folios Matthew Wilcox (Oracle)
2021-03-05 4:19 ` [PATCH v4 25/25] cachefiles: Switch to wait_page_key Matthew Wilcox (Oracle)
2021-03-17 17:45 ` Christoph Hellwig
2021-03-13 20:36 ` [PATCH v4 00/25] Page folios Andrew Morton
2021-03-14 2:30 ` Matthew Wilcox
2021-03-14 3:09 ` Hugh Dickins
[not found] ` <20210315115501.7rmzaan2hxsqowgq@box>
2021-03-15 13:45 ` Matthew Wilcox
[not found] ` <YE9VLGl50hLIJHci@dhcp22.suse.cz>
2021-03-15 19:09 ` Christoph Hellwig
2021-03-15 19:40 ` Matthew Wilcox
2021-03-15 22:27 ` Dave Chinner
2021-03-17 17:48 ` Christoph Hellwig
2021-03-15 21:33 ` Andi Kleen
2021-03-19 4:01 ` Matthew Wilcox
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