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Wed, 26 Aug 2020 09:28:01 -0700 (PDT) Date: Wed, 26 Aug 2020 12:26:47 -0400 From: Johannes Weiner To: Matthew Wilcox Cc: linux-mm@kvack.org, Andrew Morton , Hugh Dickins , William Kucharski , Jani Nikula , Alexey Dobriyan , Chris Wilson , Matthew Auld , Huang Ying , intel-gfx@lists.freedesktop.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/8] mm: Use find_get_swap_page in memcontrol Message-ID: <20200826162647.GA995045@cmpxchg.org> References: <20200819184850.24779-1-willy@infradead.org> <20200819184850.24779-3-willy@infradead.org> <20200826142002.GA988805@cmpxchg.org> <20200826145414.GS17456@casper.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200826145414.GS17456@casper.infradead.org> X-Rspamd-Queue-Id: E57331801651D X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam02 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Aug 26, 2020 at 03:54:14PM +0100, Matthew Wilcox wrote: > 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; > > ... > } Yeah, I like the idea of two lookups if we can't find a good name for the operation that combines them. I'd just bubble the control flow that links them up to the callsite - that still seems plenty compact for two callsites, and keeps all the shmem magic in shmem code: page = find_get_entry(mapping, index); if (xa_is_value(page)) if (shmem_mapping(mapping)) page = lookup_shmem_swap_cache(page); else page = NULL; So close to making radix_to_swp_entry() & co. private to shmem.c, too - if it weren't for force_shm_swapin_readahead(). Ah well.