linux-kernel - Re: [PATCH 2/8] mm: Use find_get_swap

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Message-ID: <20200826145414.GS17456@casper.infradead.org>
Date:   Wed, 26 Aug 2020 15:54:14 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        William Kucharski <william.kucharski@...cle.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Matthew Auld <matthew.auld@...el.com>,
        Huang Ying <ying.huang@...el.com>,
        intel-gfx@...ts.freedesktop.org, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/8] mm: Use find_get_swap_page in memcontrol

On Wed, Aug 26, 2020 at 10:20:02AM -0400, Johannes Weiner wrote:
> On Wed, Aug 19, 2020 at 07:48:44PM +0100, Matthew Wilcox (Oracle) wrote:
> > +	return find_get_swap_page(vma->vm_file->f_mapping,
> > +			linear_page_index(vma, addr));
> 
> The refactor makes sense to me, but the name is confusing. We're not
> looking for a swap page, we're primarily looking for a file page in
> the page cache mapping that's handed in. Only in the special case
> where it's a shmem mapping and there is a swap entry do we consult the
> auxiliary swap cache.
> 
> How about find_get_page_or_swapcache()? find_get_page_shmemswap()?
> Maybe you have a better idea. It's a fairly specialized operation that
> isn't widely used, so a longer name isn't a bad thing IMO.

Yeah, I had trouble with the naming here too.

get_page_even_from_swap()
find_get_shmem_page()

or maybe refactor the whole thing:

	struct page *page = find_get_entry(mapping, index);
	page = find_swap_page(mapping, page);

struct page *find_swap_page(struct address_space *mapping, struct page *page)
{
	swp_entry_t swp;
	struct swap_info_struct *si;

	if (!xa_is_value(page))
		return page;
	if (!shmem_mapping(mapping))
		return NULL;

	...
}