linux-kernel - Re: [PATCH v10 33/33] mm: Add folio

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Message-ID: <YK9YzS1T3xp3QI8/@infradead.org>
Date:   Thu, 27 May 2021 09:31:09 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc:     akpm@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v10 33/33] mm: Add folio_mapped

On Tue, May 11, 2021 at 10:47:35PM +0100, Matthew Wilcox (Oracle) wrote:
> This function is the equivalent of page_mapped().  It is slightly
> shorter as we do not need to handle the PageTail() case.  Reimplement
> page_mapped() as a wrapper around folio_mapped().

No byte savings numbers as for the other patches?

The patch itself looks good, although I'd go for a slightly easier
readable structure:

bool folio_mapped(struct folio *folio)
{
	if (folio_single(folio))
		return atomic_read(&folio->_mapcount) >= 0;

	if (atomic_read(compound_mapcount_ptr(&folio->page)) >= 0)
		return true;

	if (!folio_hugetlb(folio)) {
		unsigned long i;

		for (i = 0; i < folio_nr_pages(folio); i++)
			if (atomic_read(&folio_page(folio, i)->_mapcount) >= 0)
 				return true;
 	}
 	return false;
 }

 Shouldn't we also have a folio version of compound_mapcount_ptr?