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bh=QKow0BurBsftNBbjIsOOxipwJBgGGBGlzMsjaeUzlII=; b=nI0sHuYXvEq+qIFqQV1QTxmIqHyVHkPe73OO8w2MnNN3YccLOas99ReS3gCfTplPz87aBf YxFw+N+xmX85S/8zbo/uxf4NpM6AQ9dLHIwQ9CJuQYcfxMFY8jndzXq6LFgkxlAJNDRVvL Ikg72JW0jdFBWQD/jMvS+L8cPh/QdbI= Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=QkkCc5ix; spf=pass (imf29.hostedemail.com: domain of will@kernel.org designates 145.40.68.75 as permitted sender) smtp.mailfrom=will@kernel.org; dmarc=pass (policy=none) header.from=kernel.org X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: 4emun9731ny14wzpaji3jdspkn7usqsb X-Rspamd-Queue-Id: 6A39212004C X-HE-Tag: 1657124267-142904 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, Jul 05, 2022 at 09:07:59PM +0800, Huacai Chen wrote: > On Tue, Jul 5, 2022 at 5:29 PM Will Deacon wrote: > > On Mon, Jul 04, 2022 at 07:25:25PM +0800, Huacai Chen wrote: > > > diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c > > > index 33e2a1ceee72..6f2e40bb695d 100644 > > > --- a/mm/sparse-vmemmap.c > > > +++ b/mm/sparse-vmemmap.c > > > @@ -686,6 +686,60 @@ int __meminit vmemmap_populate_basepages(unsigned long start, unsigned long end, > > > return vmemmap_populate_range(start, end, node, altmap, NULL); > > > } > > > > > > +void __weak __meminit vmemmap_set_pmd(pmd_t *pmd, void *p, int node, > > > + unsigned long addr, unsigned long next) > > > +{ > > > +} > > > + > > > +int __weak __meminit vmemmap_check_pmd(pmd_t *pmd, int node, unsigned long addr, > > > + unsigned long next) > > > +{ > > > + return 0; > > > +} > > > + > > > +int __meminit vmemmap_populate_hugepages(unsigned long start, unsigned long end, > > > + int node, struct vmem_altmap *altmap) > > > +{ > > > + unsigned long addr; > > > + unsigned long next; > > > + pgd_t *pgd; > > > + p4d_t *p4d; > > > + pud_t *pud; > > > + pmd_t *pmd; > > > + > > > + for (addr = start; addr < end; addr = next) { > > > + next = pmd_addr_end(addr, end); > > > + > > > + pgd = vmemmap_pgd_populate(addr, node); > > > + if (!pgd) > > > + return -ENOMEM; > > > + > > > + p4d = vmemmap_p4d_populate(pgd, addr, node); > > > + if (!p4d) > > > + return -ENOMEM; > > > + > > > + pud = vmemmap_pud_populate(p4d, addr, node); > > > + if (!pud) > > > + return -ENOMEM; > > > + > > > + pmd = pmd_offset(pud, addr); > > > + if (pmd_none(READ_ONCE(*pmd))) { > > > + void *p; > > > + > > > + p = vmemmap_alloc_block_buf(PMD_SIZE, node, altmap); > > > + if (p) { > > > + vmemmap_set_pmd(pmd, p, node, addr, next); > > > + continue; > > > + } else if (altmap) > > > + return -ENOMEM; /* no fallback */ > > > > Why do you return -ENOMEM if 'altmap' here? That seems to be different to > > what we currently have on arm64 and it's not clear to me why we're happy > > with an altmap for the pmd case, but not for the pte case. > The generic version is the same as X86. It seems that ARM64 always > fallback whether there is an altmap, but X86 only fallback in the no > altmap case. I don't know the reason of X86, can Dan Williams give > some explaination? Right, I think we need to understand the new behaviour here before we adopt it on arm64. Will