linux-kernel - Re: [PATCH 2/9] mm/hugetlb: convert hugetlbfs_pagecache

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Date:   Fri, 20 Jan 2023 15:40:34 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Sidhartha Kumar <sidhartha.kumar@...cle.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, songmuchun@...edance.com,
        jhubbard@...dia.com
Subject: Re: [PATCH 2/9] mm/hugetlb: convert hugetlbfs_pagecache_present() to
 folios

On 01/20/23 05:43, Matthew Wilcox wrote:
> On Thu, Jan 19, 2023 at 01:14:39PM -0800, Sidhartha Kumar wrote:
> > +++ b/mm/hugetlb.c
> > @@ -5653,15 +5653,15 @@ static bool hugetlbfs_pagecache_present(struct hstate *h,
> >  {
> >  	struct address_space *mapping;
> >  	pgoff_t idx;
> > -	struct page *page;
> > +	struct folio *folio;
> >  
> >  	mapping = vma->vm_file->f_mapping;
> >  	idx = vma_hugecache_offset(h, vma, address);
> >  
> > -	page = find_get_page(mapping, idx);
> > -	if (page)
> > -		put_page(page);
> > -	return page != NULL;
> > +	folio = filemap_get_folio(mapping, idx);
> > +	if (folio)
> > +		folio_put(folio);
> > +	return folio != NULL;
> >  }
> 
> Seems to me this function could be ...
> 
> 	struct address_space *mapping = vma->vm_file->f_mapping;
> 	pgoff_t index = vma_hugecache_offset(h, vma, address);
> 	bool present;
> 
> 	rcu_read_lock();
> 	present = page_cache_next_miss(mapping, index, 1) != index;
> 	rcu_read_unlock();
> 
> 	return present;
> 
> No need to get/drop a refcount on the folio.  It's a bit similar to
> filemap_range_has_page(), but the API is wrong.  Maybe there's room
> for a little refactoring here.

Thanks Matthew, I did not know those APIs were available.  Perhaps just
use page_cache_next_miss as suggested above for now.

FYI - There is the same pattern in hugetlbfs_fallocate()

		/* See if already present in mapping to avoid alloc/free */
		folio = filemap_get_folio(mapping, index);
		if (folio) {
			folio_put(folio);
			mutex_unlock(&hugetlb_fault_mutex_table[hash]);
			hugetlb_drop_vma_policy(&pseudo_vma);
			continue;
		}

-- 
Mike Kravetz