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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 42510C433EF for ; Wed, 20 Apr 2022 17:53:55 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 7A59F6B0071; Wed, 20 Apr 2022 13:53:54 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 72F636B0073; Wed, 20 Apr 2022 13:53:54 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5CE406B0074; Wed, 20 Apr 2022 13:53:54 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.hostedemail.com [64.99.140.25]) by kanga.kvack.org (Postfix) with ESMTP id 475466B0071 for ; Wed, 20 Apr 2022 13:53:54 -0400 (EDT) Received: from smtpin15.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay12.hostedemail.com (Postfix) with ESMTP id 10146122B1A for ; Wed, 20 Apr 2022 17:53:54 +0000 (UTC) X-FDA: 79378005588.15.FC59C25 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by imf15.hostedemail.com (Postfix) with ESMTP id EC113A0018 for ; Wed, 20 Apr 2022 17:53:51 +0000 (UTC) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id C73AA61ACE; Wed, 20 Apr 2022 17:53:52 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 31D90C385A1; Wed, 20 Apr 2022 17:53:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1650477232; bh=rPJ14Ac12EFXoPf+Opo+3BFlBnnBFWwCWA10Yw/roM4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=DNJCvLcrczQXOR26pFils3zVtLSX+a22jx4HK/7JTzY0VRs1YnJUYbApEMP3PqiuO htygMdsMH95ETCitJaEoVaHUfM7AO3em3vx2FrjIVfQLW+QjJZ8hO/BC2evMuPRso2 HNt6Cm9ixu01cWQrjkNlTJbny/ezw3kHmxEOcZMU4TxTOJoy07BP4YTSveRhrW5m86 w4m+vpYFWBy5Y6rKjRaQQoReY3y0rT6b1n0UfLvAGWJTNUhx93kzLRbXrxx3Iwm5i+ 3vjQMEHpyrRDLyYMgIk0ADlpSsLo+uyt3DSecmRMNI6eY+hMbq3LW7M2FosswmmNPC Ao9k2Wu7rcS7A== Date: Wed, 20 Apr 2022 10:53:51 -0700 From: "Darrick J. Wong" To: Shiyang Ruan Cc: linux-kernel@vger.kernel.org, linux-xfs@vger.kernel.org, nvdimm@lists.linux.dev, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, dan.j.williams@intel.com, david@fromorbit.com, hch@infradead.org, jane.chu@oracle.com, Christoph Hellwig Subject: Re: [PATCH v13 4/7] fsdax: Introduce dax_lock_mapping_entry() Message-ID: <20220420175351.GX17025@magnolia> References: <20220419045045.1664996-1-ruansy.fnst@fujitsu.com> <20220419045045.1664996-5-ruansy.fnst@fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220419045045.1664996-5-ruansy.fnst@fujitsu.com> X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: EC113A0018 X-Rspam-User: Authentication-Results: imf15.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=DNJCvLcr; dmarc=pass (policy=none) header.from=kernel.org; spf=pass (imf15.hostedemail.com: domain of djwong@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=djwong@kernel.org X-Stat-Signature: jcrdi4ciwznsu8mrz444fecbh78bjxum X-HE-Tag: 1650477231-328332 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 Tue, Apr 19, 2022 at 12:50:42PM +0800, Shiyang Ruan wrote: > The current dax_lock_page() locks dax entry by obtaining mapping and > index in page. To support 1-to-N RMAP in NVDIMM, we need a new function > to lock a specific dax entry corresponding to this file's mapping,index. > And output the page corresponding to the specific dax entry for caller > use. > > Signed-off-by: Shiyang Ruan > Reviewed-by: Christoph Hellwig > --- > fs/dax.c | 63 +++++++++++++++++++++++++++++++++++++++++++++ > include/linux/dax.h | 15 +++++++++++ > 2 files changed, 78 insertions(+) > > diff --git a/fs/dax.c b/fs/dax.c > index 1ac12e877f4f..57efd3f73655 100644 > --- a/fs/dax.c > +++ b/fs/dax.c > @@ -455,6 +455,69 @@ void dax_unlock_page(struct page *page, dax_entry_t cookie) > dax_unlock_entry(&xas, (void *)cookie); > } > > +/* > + * dax_lock_mapping_entry - Lock the DAX entry corresponding to a mapping > + * @mapping: the file's mapping whose entry we want to lock > + * @index: the offset within this file > + * @page: output the dax page corresponding to this dax entry > + * > + * Return: A cookie to pass to dax_unlock_mapping_entry() or 0 if the entry > + * could not be locked. > + */ > +dax_entry_t dax_lock_mapping_entry(struct address_space *mapping, pgoff_t index, > + struct page **page) > +{ > + XA_STATE(xas, NULL, 0); > + void *entry; > + > + rcu_read_lock(); > + for (;;) { > + entry = NULL; > + if (!dax_mapping(mapping)) > + break; > + > + xas.xa = &mapping->i_pages; > + xas_lock_irq(&xas); > + xas_set(&xas, index); > + entry = xas_load(&xas); > + if (dax_is_locked(entry)) { > + rcu_read_unlock(); > + wait_entry_unlocked(&xas, entry); > + rcu_read_lock(); > + continue; > + } > + if (!entry || > + dax_is_zero_entry(entry) || dax_is_empty_entry(entry)) { > + /* > + * Because we are looking for entry from file's mapping > + * and index, so the entry may not be inserted for now, > + * or even a zero/empty entry. We don't think this is > + * an error case. So, return a special value and do > + * not output @page. > + */ > + entry = (void *)~0UL; In this case we exit to the caller with the magic return value, having not set *page. Either the comment for this function should note that the caller must set *page to a known value (NULL?) before the call, or we should set *page = NULL here. AFAICT the callers in this series initialize page to NULL before passing in &page, so I think the comment update would be fine. With the **page requirement documented, Reviewed-by: Darrick J. Wong --D > + } else { > + *page = pfn_to_page(dax_to_pfn(entry)); > + dax_lock_entry(&xas, entry); > + } > + xas_unlock_irq(&xas); > + break; > + } > + rcu_read_unlock(); > + return (dax_entry_t)entry; > +} > + > +void dax_unlock_mapping_entry(struct address_space *mapping, pgoff_t index, > + dax_entry_t cookie) > +{ > + XA_STATE(xas, &mapping->i_pages, index); > + > + if (cookie == ~0UL) > + return; > + > + dax_unlock_entry(&xas, (void *)cookie); > +} > + > /* > * Find page cache entry at given index. If it is a DAX entry, return it > * with the entry locked. If the page cache doesn't contain an entry at > diff --git a/include/linux/dax.h b/include/linux/dax.h > index 9c426a207ba8..c152f315d1c9 100644 > --- a/include/linux/dax.h > +++ b/include/linux/dax.h > @@ -143,6 +143,10 @@ struct page *dax_layout_busy_page(struct address_space *mapping); > struct page *dax_layout_busy_page_range(struct address_space *mapping, loff_t start, loff_t end); > dax_entry_t dax_lock_page(struct page *page); > void dax_unlock_page(struct page *page, dax_entry_t cookie); > +dax_entry_t dax_lock_mapping_entry(struct address_space *mapping, > + unsigned long index, struct page **page); > +void dax_unlock_mapping_entry(struct address_space *mapping, > + unsigned long index, dax_entry_t cookie); > #else > static inline struct page *dax_layout_busy_page(struct address_space *mapping) > { > @@ -170,6 +174,17 @@ static inline dax_entry_t dax_lock_page(struct page *page) > static inline void dax_unlock_page(struct page *page, dax_entry_t cookie) > { > } > + > +static inline dax_entry_t dax_lock_mapping_entry(struct address_space *mapping, > + unsigned long index, struct page **page) > +{ > + return 0; > +} > + > +static inline void dax_unlock_mapping_entry(struct address_space *mapping, > + unsigned long index, dax_entry_t cookie) > +{ > +} > #endif > > int dax_zero_range(struct inode *inode, loff_t pos, loff_t len, bool *did_zero, > -- > 2.35.1 > > >