linux-kernel - Re: [PATCH v10 01/10] fs: Allow fine-grained control of folio sizes

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Message-ID: <20240722141957.yog434qio6okkdiq@quentin>
Date: Mon, 22 Jul 2024 14:19:57 +0000
From: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: david@...morbit.com, chandan.babu@...cle.com, djwong@...nel.org,
	brauner@...nel.org, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, yang@...amperecomputing.com,
	linux-mm@...ck.org, john.g.garry@...cle.com,
	linux-fsdevel@...r.kernel.org, hare@...e.de, p.raghav@...sung.com,
	mcgrof@...nel.org, gost.dev@...sung.com, cl@...amperecomputing.com,
	linux-xfs@...r.kernel.org, ryan.roberts@....com, hch@....de,
	Zi Yan <ziy@...dia.com>
Subject: Re: [PATCH v10 01/10] fs: Allow fine-grained control of folio sizes

@willy:

I want to clarify before sending the next round of patches as I didn't
get any reply in the previous email.

IIUC your comments properly:

- I will go back to silent clamping in mapping_set_folio_order_range as
  before and remove VM_WARN_ONCE().

- I will move the mapping_max_folio_size_supported() to patch 10, and FSs
  can use them to check for the max block size that can be supported and
  take the respective action.

--
Pankaj

On Tue, Jul 16, 2024 at 04:26:10PM +0100, Matthew Wilcox wrote:
> On Mon, Jul 15, 2024 at 11:44:48AM +0200, Pankaj Raghav (Samsung) wrote:
> > +/*
> > + * mapping_max_folio_size_supported() - Check the max folio size supported
> > + *
> > + * The filesystem should call this function at mount time if there is a
> > + * requirement on the folio mapping size in the page cache.
> > + */
> > +static inline size_t mapping_max_folio_size_supported(void)
> > +{
> > +	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
> > +		return 1U << (PAGE_SHIFT + MAX_PAGECACHE_ORDER);
> > +	return PAGE_SIZE;
> > +}
> 
> There's no need for this to be part of this patch.  I've removed stuff
> from this patch before that's not needed, please stop adding unnecessary
> functions.  This would logically be part of patch 10.
> 
> > +static inline void mapping_set_folio_order_range(struct address_space *mapping,
> > +						 unsigned int min,
> > +						 unsigned int max)
> > +{
> > +	if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
> > +		return;
> > +
> > +	if (min > MAX_PAGECACHE_ORDER) {
> > +		VM_WARN_ONCE(1,
> > +	"min order > MAX_PAGECACHE_ORDER. Setting min_order to MAX_PAGECACHE_ORDER");
> > +		min = MAX_PAGECACHE_ORDER;
> > +	}
> 
> This is really too much.  It's something that will never happen.  Just
> delete the message.
> 
> > +	if (max > MAX_PAGECACHE_ORDER) {
> > +		VM_WARN_ONCE(1,
> > +	"max order > MAX_PAGECACHE_ORDER. Setting max_order to MAX_PAGECACHE_ORDER");
> > +		max = MAX_PAGECACHE_ORDER;
> 
> Absolutely not.  If the filesystem declares it can support a block size
> of 4TB, then good for it.  We just silently clamp it.
>