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 B79DCC433EF for ; Wed, 29 Jun 2022 16:21:01 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 091318E0009; Wed, 29 Jun 2022 12:21:01 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 040B66B0080; Wed, 29 Jun 2022 12:21:00 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E4B148E0009; Wed, 29 Jun 2022 12:21:00 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id D36BC6B007E for ; Wed, 29 Jun 2022 12:21:00 -0400 (EDT) Received: from smtpin14.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay13.hostedemail.com (Postfix) with ESMTP id 9CFE460293 for ; Wed, 29 Jun 2022 16:21:00 +0000 (UTC) X-FDA: 79631787480.14.AD2B11C Received: from mail-pj1-f41.google.com (mail-pj1-f41.google.com [209.85.216.41]) by imf27.hostedemail.com (Postfix) with ESMTP id 3860F40046 for ; Wed, 29 Jun 2022 16:21:00 +0000 (UTC) Received: by mail-pj1-f41.google.com with SMTP id w19-20020a17090a8a1300b001ec79064d8dso19958346pjn.2 for ; Wed, 29 Jun 2022 09:20:59 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=4L513XqZtWyyXUpVXOUXgB+Yz/acGiL267AM+UDrZNg=; b=qkxMekTBZItQ/zNOCfAfRi3/DzuqeFleQ6plx9DO7uL6976c/L4h/6OGCmIOfGlmEF 0m8LQRebbvSxS0fZazNR+by/7NyILW7ChgGq+TBwqfBNOwumgMw0E19ylcDVWn7EM+eX WtjfN6xjq9iMM+rSZzlA3e4D+LBNLytD2d7XI6M9+JIMDiUhMcYB7cPbOv6kObSfQVre ejdLKaTZ8w7iRdor6E1YZjUaocwm442pWZAd0xsOda93WTJu1lYhoj7HD17qBBDZjn3z Ze95ZmXGmOrEaXcR/EjqX2eT0gLlY/HN2beoynH/hn7WysVc4nObdGZ09Lb53SCu2xsm J2+w== 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=4L513XqZtWyyXUpVXOUXgB+Yz/acGiL267AM+UDrZNg=; b=UMnz7SuiIJueEa0WaroT+GY6brIofq+RYqqFgVVuudAV77KBaJZg8CwY405n8+JbXp thk3MiJeAfrEqQVQnLZVlnq1/ebGni0eng66FieJx3l9T/e2F/buA4/wPGii3w8FQIQa YxTVyhGL7/44n2ctf8VqccT1T+XOVIL9xiTf/5vUlivtxaxx/jN1THOtUtQ+vebPqP9H MBXe3iCEa9eEiifolkkQGbo8WqRkhfMC1csO9uOVmkS+Om615Y9pKimH1nxCF4zcNCAn NOfgJlRJ6xYCD8xhYW8pKAtc8yqLmC6rJ5JSJ4C/Q74a2KTQDPJWniH5boi9qdCXp3qI LitQ== X-Gm-Message-State: AJIora9iNDRnW6wo0YqBLqw+MDhvHUIPQlPi7AvV16RsNvOE3G5b9Lq0 ZPdgqWzWkcqufCr+YLCDqyEvMO4qWRTmIlCs6he5zA== X-Google-Smtp-Source: AGRyM1s9UrL6/EZvDiVNq4UVHYHW7ilzb1nDLUZxhfQu9FHb+sgfsvcNZQnmwK/2jxuacobw4Y9WcAxxSMWELyNTsb8= X-Received: by 2002:a17:902:e94f:b0:16a:214e:46c1 with SMTP id b15-20020a170902e94f00b0016a214e46c1mr9880791pll.89.1656519659052; Wed, 29 Jun 2022 09:20:59 -0700 (PDT) MIME-Version: 1.0 References: <20220624173656.2033256-1-jthoughton@google.com> <20220624173656.2033256-13-jthoughton@google.com> <54e46486-8886-f5d4-4900-8a250bb5e805@nutanix.com> In-Reply-To: <54e46486-8886-f5d4-4900-8a250bb5e805@nutanix.com> From: James Houghton Date: Wed, 29 Jun 2022 09:20:48 -0700 Message-ID: Subject: Re: [RFC PATCH 12/26] hugetlb: add HugeTLB splitting functionality To: "manish.mishra" Cc: Mike Kravetz , Muchun Song , Peter Xu , David Hildenbrand , David Rientjes , Axel Rasmussen , Mina Almasry , Jue Wang , "Dr . David Alan Gilbert" , linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" ARC-Authentication-Results: i=1; imf27.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=qkxMekTB; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf27.hostedemail.com: domain of jthoughton@google.com designates 209.85.216.41 as permitted sender) smtp.mailfrom=jthoughton@google.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1656519660; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=4L513XqZtWyyXUpVXOUXgB+Yz/acGiL267AM+UDrZNg=; b=oR2ajoQEx9IGraGGyW5nuOQoiVWmgxgTWvzDbql7SQT6Z76MhnGICXf9wmHDxC2a0pj7lb 5BcuRv71i1wd5CAcL6ifwUxhnCSjrcK7+v4n3V2jtaosxzyzFw2Xvxv7uiHgTY/Wqe9D0F jIl09FTfiWq/EL6E2RyaM7sPknT23Z4= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1656519660; a=rsa-sha256; cv=none; b=JCwdoOe7dTUthysVqcpO4cdOFRZg2rdVlIbNIV2manN0zOr9gO8E2Q2E4JpLV44Cz15IBi /SN2AUfGmiNYKHExRTMmeHftYbIJhjany5XmRRukyJqAJMnSMjB7bmqCZh6NJcIyEj9q2X aoLIwV52Q63qUEVdjqV1SXg4MgsJkvs= X-Stat-Signature: 7tgtk8jd65r7n3jak7efnd991rsn3d1y X-Rspamd-Queue-Id: 3860F40046 Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=qkxMekTB; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf27.hostedemail.com: domain of jthoughton@google.com designates 209.85.216.41 as permitted sender) smtp.mailfrom=jthoughton@google.com X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1656519660-795789 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 29, 2022 at 7:33 AM manish.mishra wrote: > > > On 24/06/22 11:06 pm, James Houghton wrote: > > The new function, hugetlb_split_to_shift, will optimally split the page > > table to map a particular address at a particular granularity. > > > > This is useful for punching a hole in the mapping and for mapping small > > sections of a HugeTLB page (via UFFDIO_CONTINUE, for example). > > > > Signed-off-by: James Houghton > > --- > > mm/hugetlb.c | 122 +++++++++++++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 122 insertions(+) > > > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > > index 3ec2a921ee6f..eaffe7b4f67c 100644 > > --- a/mm/hugetlb.c > > +++ b/mm/hugetlb.c > > @@ -102,6 +102,18 @@ struct mutex *hugetlb_fault_mutex_table ____cacheline_aligned_in_smp; > > /* Forward declaration */ > > static int hugetlb_acct_memory(struct hstate *h, long delta); > > > > +/* > > + * Find the subpage that corresponds to `addr` in `hpage`. > > + */ > > +static struct page *hugetlb_find_subpage(struct hstate *h, struct page *hpage, > > + unsigned long addr) > > +{ > > + size_t idx = (addr & ~huge_page_mask(h))/PAGE_SIZE; > > + > > + BUG_ON(idx >= pages_per_huge_page(h)); > > + return &hpage[idx]; > > +} > > + > > static inline bool subpool_is_free(struct hugepage_subpool *spool) > > { > > if (spool->count) > > @@ -7044,6 +7056,116 @@ static unsigned int __shift_for_hstate(struct hstate *h) > > for ((tmp_h) = hstate; (shift) = __shift_for_hstate(tmp_h), \ > > (tmp_h) <= &hstates[hugetlb_max_hstate]; \ > > (tmp_h)++) > > + > > +/* > > + * Given a particular address, split the HugeTLB PTE that currently maps it > > + * so that, for the given address, the PTE that maps it is `desired_shift`. > > + * This function will always split the HugeTLB PTE optimally. > > + * > > + * For example, given a HugeTLB 1G page that is mapped from VA 0 to 1G. If we > > + * call this function with addr=0 and desired_shift=PAGE_SHIFT, will result in > > + * these changes to the page table: > > + * 1. The PUD will be split into 2M PMDs. > > + * 2. The first PMD will be split again into 4K PTEs. > > + */ > > +static int hugetlb_split_to_shift(struct mm_struct *mm, struct vm_area_struct *vma, > > + const struct hugetlb_pte *hpte, > > + unsigned long addr, unsigned long desired_shift) > > +{ > > + unsigned long start, end, curr; > > + unsigned long desired_sz = 1UL << desired_shift; > > + struct hstate *h = hstate_vma(vma); > > + int ret; > > + struct hugetlb_pte new_hpte; > > + struct mmu_notifier_range range; > > + struct page *hpage = NULL; > > + struct page *subpage; > > + pte_t old_entry; > > + struct mmu_gather tlb; > > + > > + BUG_ON(!hpte->ptep); > > + BUG_ON(hugetlb_pte_size(hpte) == desired_sz); > > + > > + start = addr & hugetlb_pte_mask(hpte); > > + end = start + hugetlb_pte_size(hpte); > > + > > + i_mmap_assert_write_locked(vma->vm_file->f_mapping); > > + > > + BUG_ON(!hpte->ptep); > > + /* This function only works if we are looking at a leaf-level PTE. */ > > + BUG_ON(!hugetlb_pte_none(hpte) && !hugetlb_pte_present_leaf(hpte)); > > + > > + /* > > + * Clear the PTE so that we will allocate the PT structures when > > + * walking the page table. > > + */ > > + old_entry = huge_ptep_get_and_clear(mm, start, hpte->ptep); > > Sorry missed it last time, what if hgm mapping present here and current hpte is > > at higher level. Where we will clear and free child page-table pages. > > I see it does not happen in huge_ptep_get_and_clear. This shouldn't happen because earlier we have BUG_ON(!hugetlb_pte_none(hpte) && !hugetlb_pte_present_leaf(hpte)); i.e., hpte must either be none or present and leaf-level. > > > + > > + if (!huge_pte_none(old_entry)) > > + hpage = pte_page(old_entry); > > + > > + BUG_ON(!IS_ALIGNED(start, desired_sz)); > > + BUG_ON(!IS_ALIGNED(end, desired_sz)); > > + > > + for (curr = start; curr < end;) { > > + struct hstate *tmp_h; > > + unsigned int shift; > > + > > + for_each_hgm_shift(h, tmp_h, shift) { > > + unsigned long sz = 1UL << shift; > > + > > + if (!IS_ALIGNED(curr, sz) || curr + sz > end) > > + continue; > > + /* > > + * If we are including `addr`, we need to make sure > > + * splitting down to the correct size. Go to a smaller > > + * size if we are not. > > + */ > > + if (curr <= addr && curr + sz > addr && > > + shift > desired_shift) > > + continue; > > + > > + /* > > + * Continue the page table walk to the level we want, > > + * allocate PT structures as we go. > > + */ > > + hugetlb_pte_copy(&new_hpte, hpte); > > + ret = hugetlb_walk_to(mm, &new_hpte, curr, sz, > > + /*stop_at_none=*/false); > > + if (ret) > > + goto err; > > + BUG_ON(hugetlb_pte_size(&new_hpte) != sz); > > + if (hpage) { > > + pte_t new_entry; > > + > > + subpage = hugetlb_find_subpage(h, hpage, curr); > > + new_entry = make_huge_pte_with_shift(vma, subpage, > > + huge_pte_write(old_entry), > > + shift); > > + set_huge_pte_at(mm, curr, new_hpte.ptep, new_entry); > > + } > > + curr += sz; > > + goto next; > > + } > > + /* We couldn't find a size that worked. */ > > + BUG(); > > +next: > > + continue; > > + } > > + > > + mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm, > > + start, end); > > + mmu_notifier_invalidate_range_start(&range); > > + return 0; > > +err: > > + tlb_gather_mmu(&tlb, mm); > > + /* Free any newly allocated page table entries. */ > > + hugetlb_free_range(&tlb, hpte, start, curr); > > + /* Restore the old entry. */ > > + set_huge_pte_at(mm, start, hpte->ptep, old_entry); > > + tlb_finish_mmu(&tlb); > > + return ret; > > +} > > #endif /* CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING */ > > > > /*