From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 23E7CC00307 for ; Fri, 6 Sep 2019 12:59:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EB4D721670 for ; Fri, 6 Sep 2019 12:59:32 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=shutemov-name.20150623.gappssmtp.com header.i=@shutemov-name.20150623.gappssmtp.com header.b="pY7zk/w8" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390525AbfIFM7c (ORCPT ); Fri, 6 Sep 2019 08:59:32 -0400 Received: from mail-ed1-f68.google.com ([209.85.208.68]:38365 "EHLO mail-ed1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388106AbfIFM7b (ORCPT ); Fri, 6 Sep 2019 08:59:31 -0400 Received: by mail-ed1-f68.google.com with SMTP id a23so3982633edv.5 for ; Fri, 06 Sep 2019 05:59:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=shutemov-name.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=ziEdRLsXO40ln6MLqiGodbd9Jh5bSPIFcy/rNK9Q7Ww=; b=pY7zk/w8TKLJb6+4uHUls3O2RTMWA4y90jjFogFYSGbnC8kHwBqF4z6DO/QXdoW6E0 YsRh0jq+m4bgl1o3zsg9/NasXl8gLvgOcLQDim2rH5D7UiSG7YnE6X9GM8TB25X//kwD +SSF2b4wnQxvm3Utnh9Z7HT3dwS2wSeo1b46bYUyk/y1+NUl0yV0Y+uds6NernVoc6Yn 8+BoWumqAbJSd3ZtzZ7D5zNvaB34HIoxAghzP85f84Xf5Wm3iTktI74MIr9DvzGcDMSH TBQRLtPRGk7kBF+tPeda6CcovF0XfzVGVeuJ1LBxN6w5jHJkQVV1rTsujOlSa75rktb/ k+dQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=ziEdRLsXO40ln6MLqiGodbd9Jh5bSPIFcy/rNK9Q7Ww=; b=E9Dvj/xB/qyZZD9GJqNyrddjt7zQUBVW9/x+zRiAkarbYOSqnCmnw+df2MoeFashBD CpZm3/bvRgm7OuoJF0aRc62VPjOC8GOmlrhVcYLhJ+3bO31a7BTjHANbByS1DsYiGX5J 5Ac7du5+jMgZIsA5Nt454NQqkxhfI2YlUjOJX0Q/dFkLjB/JHMyoSZuas2wcZ5jHZoPN xJxwTecgxnexukEOvrdf3otX41vP2Fd1faTvoOnPW2MxfZWWIeV/nOy5s0eDDF/eATax RFIS5uosCCZCBMWRHrYeWbdTu0JCMe343KL2bTVf3S6THuElAwg+g9f0HVqm6nKiNqQx OxZA== X-Gm-Message-State: APjAAAUTFex4HdXF70Su+U6xfYWhMpEpgPx/esrvIrRvroldrZAn4N6z n8ibizvWAMr37qotHakBh0W53g== X-Google-Smtp-Source: APXvYqyM60s24Ukh0h3LJMSfouaIHNvU1YMuRs0W9Y4zW6Ppmqnt6NhfeH5WdCs329ssEK+X7vonxA== X-Received: by 2002:a50:981b:: with SMTP id g27mr9406727edb.105.1567774769088; Fri, 06 Sep 2019 05:59:29 -0700 (PDT) Received: from box.localdomain ([86.57.175.117]) by smtp.gmail.com with ESMTPSA id p4sm815871edc.38.2019.09.06.05.59.28 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 06 Sep 2019 05:59:28 -0700 (PDT) Received: by box.localdomain (Postfix, from userid 1000) id 7E46B1049F1; Fri, 6 Sep 2019 15:59:28 +0300 (+03) Date: Fri, 6 Sep 2019 15:59:28 +0300 From: "Kirill A. Shutemov" To: Matthew Wilcox Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Song Liu , William Kucharski , Johannes Weiner Subject: Re: [PATCH 3/3] mm: Allow find_get_page to be used for large pages Message-ID: <20190906125928.urwopgpd66qibbil@box> References: <20190905182348.5319-1-willy@infradead.org> <20190905182348.5319-4-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190905182348.5319-4-willy@infradead.org> User-Agent: NeoMutt/20180716 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Thu, Sep 05, 2019 at 11:23:48AM -0700, Matthew Wilcox wrote: > From: "Matthew Wilcox (Oracle)" > > Add FGP_PMD to indicate that we're trying to find-or-create a page that > is at least PMD_ORDER in size. The internal 'conflict' entry usage > is modelled after that in DAX, but the implementations are different > due to DAX using multi-order entries and the page cache using multiple > order-0 entries. > > Signed-off-by: Matthew Wilcox (Oracle) > --- > include/linux/pagemap.h | 9 +++++ > mm/filemap.c | 82 +++++++++++++++++++++++++++++++++++++---- > 2 files changed, 84 insertions(+), 7 deletions(-) > > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h > index d2147215d415..72101811524c 100644 > --- a/include/linux/pagemap.h > +++ b/include/linux/pagemap.h > @@ -248,6 +248,15 @@ pgoff_t page_cache_prev_miss(struct address_space *mapping, > #define FGP_NOFS 0x00000010 > #define FGP_NOWAIT 0x00000020 > #define FGP_FOR_MMAP 0x00000040 > +/* > + * If you add more flags, increment FGP_ORDER_SHIFT (no further than 25). Maybe some BUILD_BUG_ON()s to ensure FGP_ORDER_SHIFT is sane? > + * Do not insert flags above the FGP order bits. > + */ > +#define FGP_ORDER_SHIFT 7 > +#define FGP_PMD ((PMD_SHIFT - PAGE_SHIFT) << FGP_ORDER_SHIFT) > +#define FGP_PUD ((PUD_SHIFT - PAGE_SHIFT) << FGP_ORDER_SHIFT) > + > +#define fgp_order(fgp) ((fgp) >> FGP_ORDER_SHIFT) > > struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset, > int fgp_flags, gfp_t cache_gfp_mask); > diff --git a/mm/filemap.c b/mm/filemap.c > index ae3c0a70a8e9..904dfabbea52 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -1572,7 +1572,71 @@ struct page *find_get_entry(struct address_space *mapping, pgoff_t offset) > > return page; > } > -EXPORT_SYMBOL(find_get_entry); > + > +static bool pagecache_is_conflict(struct page *page) > +{ > + return page == XA_RETRY_ENTRY; > +} > + > +/** > + * __find_get_page - Find and get a page cache entry. > + * @mapping: The address_space to search. > + * @offset: The page cache index. > + * @order: The minimum order of the entry to return. > + * > + * Looks up the page cache entries at @mapping between @offset and > + * @offset + 2^@order. If there is a page cache page, it is returned with Off by one? :P > + * an increased refcount unless it is smaller than @order. > + * > + * If the slot holds a shadow entry of a previously evicted page, or a > + * swap entry from shmem/tmpfs, it is returned. > + * > + * Return: the found page, a value indicating a conflicting page or %NULL if > + * there are no pages in this range. > + */ > +static struct page *__find_get_page(struct address_space *mapping, > + unsigned long offset, unsigned int order) > +{ > + XA_STATE(xas, &mapping->i_pages, offset); > + struct page *page; > + > + rcu_read_lock(); > +repeat: > + xas_reset(&xas); > + page = xas_find(&xas, offset | ((1UL << order) - 1)); Hm. '|' is confusing. What is expectation about offset? Is round_down(offset, 1UL << order) expected to be equal offset? If yes, please use '+' instead of '|'. > + if (xas_retry(&xas, page)) > + goto repeat; > + /* > + * A shadow entry of a recently evicted page, or a swap entry from > + * shmem/tmpfs. Skip it; keep looking for pages. > + */ > + if (xa_is_value(page)) > + goto repeat; > + if (!page) > + goto out; > + if (compound_order(page) < order) { > + page = XA_RETRY_ENTRY; > + goto out; > + } compound_order() is not stable if you don't have pin on the page. Check it after page_cache_get_speculative(). > + > + if (!page_cache_get_speculative(page)) > + goto repeat; > + > + /* > + * Has the page moved or been split? > + * This is part of the lockless pagecache protocol. See > + * include/linux/pagemap.h for details. > + */ > + if (unlikely(page != xas_reload(&xas))) { > + put_page(page); > + goto repeat; > + } > + page = find_subpage(page, offset); > +out: > + rcu_read_unlock(); > + > + return page; > +} > > /** > * find_lock_entry - locate, pin and lock a page cache entry > @@ -1614,12 +1678,12 @@ EXPORT_SYMBOL(find_lock_entry); > * pagecache_get_page - find and get a page reference > * @mapping: the address_space to search > * @offset: the page index > - * @fgp_flags: PCG flags > + * @fgp_flags: FGP flags > * @gfp_mask: gfp mask to use for the page cache data page allocation > * > * Looks up the page cache slot at @mapping & @offset. > * > - * PCG flags modify how the page is returned. > + * FGP flags modify how the page is returned. > * > * @fgp_flags can be: > * > @@ -1632,6 +1696,10 @@ EXPORT_SYMBOL(find_lock_entry); > * - FGP_FOR_MMAP: Similar to FGP_CREAT, only we want to allow the caller to do > * its own locking dance if the page is already in cache, or unlock the page > * before returning if we had to add the page to pagecache. > + * - FGP_PMD: We're only interested in pages at PMD granularity. If there > + * is no page here (and FGP_CREATE is set), we'll create one large enough. > + * If there is a smaller page in the cache that overlaps the PMD page, we > + * return %NULL and do not attempt to create a page. Is it really the best inteface? Maybe allow user to ask bitmask of allowed orders? For THP order-0 is fine if order-9 has failed. > * > * If FGP_LOCK or FGP_CREAT are specified then the function may sleep even > * if the GFP flags specified for FGP_CREAT are atomic. > @@ -1646,9 +1714,9 @@ struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset, > struct page *page; > > repeat: > - page = find_get_entry(mapping, offset); > - if (xa_is_value(page)) > - page = NULL; > + page = __find_get_page(mapping, offset, fgp_order(fgp_flags)); > + if (pagecache_is_conflict(page)) > + return NULL; > if (!page) > goto no_page; > > @@ -1682,7 +1750,7 @@ struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset, > if (fgp_flags & FGP_NOFS) > gfp_mask &= ~__GFP_FS; > > - page = __page_cache_alloc(gfp_mask); > + page = __page_cache_alloc_order(gfp_mask, fgp_order(fgp_flags)); > if (!page) > return NULL; > > -- > 2.23.0.rc1 > -- Kirill A. Shutemov