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 8B927C433EF for ; Wed, 16 Feb 2022 02:09:55 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id E58E36B0078; Tue, 15 Feb 2022 21:09:54 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id E08196B007B; Tue, 15 Feb 2022 21:09:54 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id CA83B6B007D; Tue, 15 Feb 2022 21:09:54 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0238.hostedemail.com [216.40.44.238]) by kanga.kvack.org (Postfix) with ESMTP id BB1306B0078 for ; Tue, 15 Feb 2022 21:09:54 -0500 (EST) Received: from smtpin15.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 7F8CC8248D52 for ; Wed, 16 Feb 2022 02:09:54 +0000 (UTC) X-FDA: 79147012308.15.131E46D Received: from mail-pl1-f177.google.com (mail-pl1-f177.google.com [209.85.214.177]) by imf21.hostedemail.com (Postfix) with ESMTP id DCF3C1C000A for ; Wed, 16 Feb 2022 02:09:53 +0000 (UTC) Received: by mail-pl1-f177.google.com with SMTP id i10so868548plr.2 for ; Tue, 15 Feb 2022 18:09:53 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=intel-com.20210112.gappssmtp.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=Q+Ju8G+K3yl0rXewZnv2N1IC9X1msq/8ymspEttmFB0=; b=g0pX+9paDLIsFTJvf2Iwxzc5R+2Rg/M68J6vnIomnLZCJeTgykYN4I9DF6JoQ/58EO ewBbo66r7K5E9FQVu8/isDoqbnf054RXWsWWuL1Jrm/fckkK3fQ2euKN7xMyWXRR/y89 1vp+hdgXJvlZLsQ159STnVV/30QoM8mBNMZWL8PsuXrmif2YeiPdoF2nqr12WWN/6D0T ZAN8Cy7+m55QT6oqbw7RZXcXjb/34BhJ00YPvdKeXsSkJ3yh95N1Oiz8LdcD7g6gGtUw uSBzOBGFL+ngPatwlg3p7PuELehciDFJqC12bD0Dym4214TAZAxI7z8RBhTFsuVU/0Ur riOg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=Q+Ju8G+K3yl0rXewZnv2N1IC9X1msq/8ymspEttmFB0=; b=ovLiqTAFPTovaKwh3CGsELlKbjZO9YzFiCCYXZU0pAh5+d6kWgLW40BQzTZHmIQd0j bvGqD1NWfF3nNhrdF6+IFlo3acYmOxeZJaFKmvBfvQqN7S91qyngNa5fLNHIS1IkDe9v j7KT4w48Rq+ynPZfcv6/085QzyJ/i1aodhbPpM5UHlGw8Hd4mJMcAfbdw2Ffs5rx9Z0R mqUZ5Lv7UeZcPH+8NLVAxSQhjxmIEhpbXu1Lo4bW/QEuzMUWkbAoTbc6Jdh1vOdVmuYn y/hPjDf4x8iLcEMEP3osoozw8Qp+l0HEw7HKgfV+yqkJKIu1wgcYCUyjnGfWqpkh1sWD aPkQ== X-Gm-Message-State: AOAM5326QmSK9EHc2d8jcJ1fjDSB+AZM1amdEvus9QlCOE6pwHZDPHCg EL85dI/mzt5ZS/jgh9r4MM8jvCWH0qttbR+gyemGhQ== X-Google-Smtp-Source: ABdhPJzwdMTmGWhsFANakVNZUZj8nYKdCXXxIPTTkPPPKXTQeyH+SCUT7kQ22lBy9f4SZLC2Pj2zCo5Yn5N8CSG4WY0= X-Received: by 2002:a17:90b:1a92:b0:1b9:8094:446b with SMTP id ng18-20020a17090b1a9200b001b98094446bmr357580pjb.93.1644977392787; Tue, 15 Feb 2022 18:09:52 -0800 (PST) MIME-Version: 1.0 References: <20220127124058.1172422-1-ruansy.fnst@fujitsu.com> <20220127124058.1172422-10-ruansy.fnst@fujitsu.com> In-Reply-To: <20220127124058.1172422-10-ruansy.fnst@fujitsu.com> From: Dan Williams Date: Tue, 15 Feb 2022 18:09:46 -0800 Message-ID: Subject: Re: [PATCH v10 9/9] fsdax: set a CoW flag when associate reflink mappings To: Shiyang Ruan Cc: Linux Kernel Mailing List , linux-xfs , Linux NVDIMM , Linux MM , linux-fsdevel , "Darrick J. Wong" , david , Christoph Hellwig , Jane Chu Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: DCF3C1C000A X-Rspam-User: Authentication-Results: imf21.hostedemail.com; dkim=pass header.d=intel-com.20210112.gappssmtp.com header.s=20210112 header.b=g0pX+9pa; spf=none (imf21.hostedemail.com: domain of dan.j.williams@intel.com has no SPF policy when checking 209.85.214.177) smtp.mailfrom=dan.j.williams@intel.com; dmarc=fail reason="No valid SPF, DKIM not aligned (relaxed)" header.from=intel.com (policy=none) X-Stat-Signature: ctcrchcr8mjyj43rfarny79t87mi4act X-Rspamd-Server: rspam03 X-HE-Tag: 1644977393-483531 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 Thu, Jan 27, 2022 at 4:41 AM Shiyang Ruan wrote: > > Introduce a PAGE_MAPPING_DAX_COW flag to support association with CoW file > mappings. In this case, the dax-RMAP already takes the responsibility > to look up for shared files by given dax page. The page->mapping is no > longer to used for rmap but for marking that this dax page is shared. > And to make sure disassociation works fine, we use page->index as > refcount, and clear page->mapping to the initial state when page->index > is decreased to 0. > > With the help of this new flag, it is able to distinguish normal case > and CoW case, and keep the warning in normal case. > > Signed-off-by: Shiyang Ruan > --- > fs/dax.c | 65 ++++++++++++++++++++++++++++++++------ > include/linux/page-flags.h | 6 ++++ > 2 files changed, 62 insertions(+), 9 deletions(-) > > diff --git a/fs/dax.c b/fs/dax.c > index 250794a5b789..88879c579c1f 100644 > --- a/fs/dax.c > +++ b/fs/dax.c > @@ -334,13 +334,46 @@ static unsigned long dax_end_pfn(void *entry) > for (pfn = dax_to_pfn(entry); \ > pfn < dax_end_pfn(entry); pfn++) > > +static inline void dax_mapping_set_cow_flag(struct address_space *mapping) > +{ > + mapping = (struct address_space *)PAGE_MAPPING_DAX_COW; > +} > + > +static inline bool dax_mapping_is_cow(struct address_space *mapping) > +{ > + return (unsigned long)mapping == PAGE_MAPPING_DAX_COW; > +} > + > /* > - * TODO: for reflink+dax we need a way to associate a single page with > - * multiple address_space instances at different linear_page_index() > - * offsets. > + * Set or Update the page->mapping with FS_DAX_MAPPING_COW flag. > + * Return true if it is an Update. > + */ > +static inline bool dax_mapping_set_cow(struct page *page) > +{ > + if (page->mapping) { > + /* flag already set */ > + if (dax_mapping_is_cow(page->mapping)) > + return false; > + > + /* > + * This page has been mapped even before it is shared, just > + * need to set this FS_DAX_MAPPING_COW flag. > + */ > + dax_mapping_set_cow_flag(page->mapping); > + return true; > + } > + /* Newly associate CoW mapping */ > + dax_mapping_set_cow_flag(page->mapping); > + return false; > +} > + > +/* > + * When it is called in dax_insert_entry(), the cow flag will indicate that > + * whether this entry is shared by multiple files. If so, set the page->mapping > + * to be FS_DAX_MAPPING_COW, and use page->index as refcount. > */ > static void dax_associate_entry(void *entry, struct address_space *mapping, > - struct vm_area_struct *vma, unsigned long address) > + struct vm_area_struct *vma, unsigned long address, bool cow) > { > unsigned long size = dax_entry_size(entry), pfn, index; > int i = 0; > @@ -352,9 +385,17 @@ static void dax_associate_entry(void *entry, struct address_space *mapping, > for_each_mapped_pfn(entry, pfn) { > struct page *page = pfn_to_page(pfn); > > - WARN_ON_ONCE(page->mapping); > - page->mapping = mapping; > - page->index = index + i++; > + if (cow) { > + if (dax_mapping_set_cow(page)) { > + /* Was normal, now updated to CoW */ > + page->index = 2; > + } else > + page->index++; > + } else { > + WARN_ON_ONCE(page->mapping); > + page->mapping = mapping; > + page->index = index + i++; > + } > } > } > > @@ -370,7 +411,12 @@ static void dax_disassociate_entry(void *entry, struct address_space *mapping, > struct page *page = pfn_to_page(pfn); > > WARN_ON_ONCE(trunc && page_ref_count(page) > 1); > - WARN_ON_ONCE(page->mapping && page->mapping != mapping); > + if (!dax_mapping_is_cow(page->mapping)) { > + /* keep the CoW flag if this page is still shared */ > + if (page->index-- > 0) > + continue; > + } else > + WARN_ON_ONCE(page->mapping && page->mapping != mapping); > page->mapping = NULL; > page->index = 0; > } > @@ -810,7 +856,8 @@ static void *dax_insert_entry(struct xa_state *xas, > void *old; > > dax_disassociate_entry(entry, mapping, false); > - dax_associate_entry(new_entry, mapping, vmf->vma, vmf->address); > + dax_associate_entry(new_entry, mapping, vmf->vma, vmf->address, > + false); Where is the caller that passes 'true'? Also when that caller arrives introduce a separate dax_associate_cow_entry() as that's easier to read than dax_associate_entry(..., true) in case someone does not remember what that boolean flag means. However, it's not clear to me that this approach is a good idea given that the filesystem is the source of truth for how many address_spaces this page mapping might be duplicated. What about a iomap_page_ops for fsdax to ask the filesystem when it is ok to clear the mapping association for a page? > /* > * Only swap our new entry into the page cache if the current > * entry is a zero page or an empty entry. If a normal PTE or > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > index 1c3b6e5c8bfd..6370d279795a 100644 > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -572,6 +572,12 @@ __PAGEFLAG(Reported, reported, PF_NO_COMPOUND) > #define PAGE_MAPPING_KSM (PAGE_MAPPING_ANON | PAGE_MAPPING_MOVABLE) > #define PAGE_MAPPING_FLAGS (PAGE_MAPPING_ANON | PAGE_MAPPING_MOVABLE) > > +/* > + * Different with flags above, this flag is used only for fsdax mode. It > + * indicates that this page->mapping is now under reflink case. > + */ > +#define PAGE_MAPPING_DAX_COW 0x1 > + > static __always_inline int PageMappingFlags(struct page *page) > { > return ((unsigned long)page->mapping & PAGE_MAPPING_FLAGS) != 0; > -- > 2.34.1 > > >