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Wed, 16 Jun 2021 16:35:29 -0700 (PDT) MIME-Version: 1.0 References: <20210325230938.30752-1-joao.m.martins@oracle.com> <20210325230938.30752-8-joao.m.martins@oracle.com> <63ce653d-4d21-c955-7b81-abba25b9e4b6@oracle.com> <99e18d97-5245-e4c7-febd-8c3781645cea@oracle.com> In-Reply-To: <99e18d97-5245-e4c7-febd-8c3781645cea@oracle.com> From: Dan Williams Date: Wed, 16 Jun 2021 16:35:18 -0700 Message-ID: Subject: Re: [PATCH v1 07/11] mm/sparse-vmemmap: populate compound pagemaps To: Joao Martins Cc: Linux MM , Ira Weiny , linux-nvdimm , Matthew Wilcox , Jason Gunthorpe , Jane Chu , Muchun Song , Mike Kravetz , Andrew Morton Content-Type: text/plain; charset="UTF-8" Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=intel-com.20150623.gappssmtp.com header.s=20150623 header.b=I468KULN; spf=none (imf05.hostedemail.com: domain of dan.j.williams@intel.com has no SPF policy when checking 209.85.210.170) smtp.mailfrom=dan.j.williams@intel.com; dmarc=fail reason="No valid SPF, DKIM not aligned (relaxed)" header.from=intel.com (policy=none) X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: D2480E000255 X-Stat-Signature: 9odi64okioxp6kkrwdth5oqngmh7wt5q X-HE-Tag: 1623886518-421874 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, Jun 16, 2021 at 8:06 AM Joao Martins wrote: > > On 5/13/21 7:45 PM, Joao Martins wrote: > > On 5/10/21 8:19 PM, Dan Williams wrote: > >> On Thu, May 6, 2021 at 4:02 AM Joao Martins wrote: > >> [..] > >>>>> +static pte_t * __meminit vmemmap_lookup_address(unsigned long addr) > >>>> > >>>> I think this can be replaced with a call to follow_pte(&init_mm...). > >>> > >>> Ah, of course! That would shorten things up too. > >> > >> Now that I look closely, I notice that function disclaims being > >> suitable as a general purpose pte lookup utility. > >> If it works for you, > >> great, but if not I think it's past time to create such a helper. I > >> know Ira is looking for one, and I contributed to the proliferation > >> when I added dev_pagemap_mapping_shift(). > >> > > There's also x86 equivalents, like lookup_address() and lookup_address_in_pgd(). > > These two don't differ that much from vmemmap_lookup_address(). > > > > I can move this to an internal place e.g. mm/internal.h > > > > The patch after this one, changes vmemmap_lookup_address() to stop at the PMD (to reuse > > that across the next sections). > > > Thinking again on this particular comment, but more on the actual need for the lookup > function. It is very specific to 1G geometry case being spread over multiple sections. > > Given section population *needs* to succeed for the followup sections to continue to be > populated, perhaps we simplify this a whole lot e.g. below comparing this patch before and > after. > > diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c > index 3d671e3e804d..c06796fcc77d 100644 > --- a/mm/sparse-vmemmap.c > +++ b/mm/sparse-vmemmap.c > @@ -554,37 +554,6 @@ static inline int __meminit vmemmap_populate_page(unsigned long addr, > int node, > return vmemmap_populate_address(addr, node, NULL, NULL, page); > } > > -static pte_t * __meminit vmemmap_lookup_address(unsigned long addr) > -{ > - pgd_t *pgd; > - p4d_t *p4d; > - pud_t *pud; > - pmd_t *pmd; > - pte_t *pte; > - > - pgd = pgd_offset_k(addr); > - if (pgd_none(*pgd)) > - return NULL; > - > - p4d = p4d_offset(pgd, addr); > - if (p4d_none(*p4d)) > - return NULL; > - > - pud = pud_offset(p4d, addr); > - if (pud_none(*pud)) > - return NULL; > - > - pmd = pmd_offset(pud, addr); > - if (pmd_none(*pmd)) > - return NULL; > - > - pte = pte_offset_kernel(pmd, addr); > - if (pte_none(*pte)) > - return NULL; > - > - return pte; > -} > - > static int __meminit vmemmap_populate_compound_pages(unsigned long start_pfn, > unsigned long start, > unsigned long end, int node, > @@ -605,8 +574,10 @@ static int __meminit vmemmap_populate_compound_pages(unsigned long > start_pfn, > offset = PFN_PHYS(start_pfn) - pgmap->ranges[pgmap->nr_range].start; > if (!IS_ALIGNED(offset, pgmap_geometry(pgmap)) && > pgmap_geometry(pgmap) > SUBSECTION_SIZE) { > - pte_t *ptep = vmemmap_lookup_address(start - PAGE_SIZE); > + pte_t *ptep; > > + addr = start - PAGE_SIZE; > + ptep = pte_offset_kernel(pmd_off_k(addr), addr); It deserves a comment about the guarantee, but looks good. > if (!ptep) > return -ENOMEM; > > The 'if (!ptep)' cannot happen in pratice AFAIU so could remove that as well. > > Thoughts?