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Tue, 25 Jan 2022 22:34:42 -0800 (PST) Date: Tue, 25 Jan 2022 22:34:42 -0800 (PST) From: David Rientjes To: Pasha Tatashin cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , pjt@google.com, weixugc@google.com, gthelen@google.com, mingo@redhat.com, will@kernel.org, rppt@kernel.org, dave.hansen@linux.intel.com, hpa@zytor.com, aneesh.kumar@linux.ibm.com, jirislaby@kernel.org, songmuchun@bytedance.com, qydwhotmail@gmail.com, hughd@google.com, ziy@nvidia.com, anshuman.khandual@arm.com Subject: Re: [PATCH v3 3/4] mm/khugepaged: unify collapse pmd clear, flush and free In-Reply-To: <20220126060514.1574935-4-pasha.tatashin@soleen.com> Message-ID: References: <20220126060514.1574935-1-pasha.tatashin@soleen.com> <20220126060514.1574935-4-pasha.tatashin@soleen.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Stat-Signature: n7o7wb7b1rf761gbt3c4rzr3auxib6ax X-Rspam-User: nil Authentication-Results: imf31.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=coV6d1V8; spf=pass (imf31.hostedemail.com: domain of rientjes@google.com designates 209.85.216.44 as permitted sender) smtp.mailfrom=rientjes@google.com; dmarc=pass (policy=reject) header.from=google.com X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: C805420004 X-HE-Tag: 1643178884-190501 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, 26 Jan 2022, Pasha Tatashin wrote: > Unify the code that flushes, clears pmd entry, and frees the PTE table > level into a new function collapse_and_free_pmd(). > > This clean-up is useful as in the next patch we will add another call to > this function to iterate through PTE prior to freeing the level for page > table check. > > Signed-off-by: Pasha Tatashin Acked-by: David Rientjes One nit below. > --- > mm/khugepaged.c | 32 ++++++++++++++++---------------- > 1 file changed, 16 insertions(+), 16 deletions(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 35f14d0a00a6..440112355ffe 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -1416,6 +1416,17 @@ static int khugepaged_add_pte_mapped_thp(struct mm_struct *mm, > return 0; > } > > +static void collapse_and_free_pmd(struct mm_struct *mm, struct vm_area_struct *vma, > + unsigned long addr, pmd_t *pmdp) > +{ > + spinlock_t *ptl = pmd_lock(vma->vm_mm, pmdp); > + pmd_t pmd = pmdp_collapse_flush(vma, addr, pmdp); > + > + spin_unlock(ptl); No strong objection, but I think the typical style would be to declare the local variables separately and avoid mixing the code, especially in cases when taking locks (and not just initializing the local variables). > + mm_dec_nr_ptes(mm); > + pte_free(mm, pmd_pgtable(pmd)); > +} > + > /** > * collapse_pte_mapped_thp - Try to collapse a pte-mapped THP for mm at > * address haddr. > @@ -1433,7 +1444,7 @@ void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr) > struct vm_area_struct *vma = find_vma(mm, haddr); > struct page *hpage; > pte_t *start_pte, *pte; > - pmd_t *pmd, _pmd; > + pmd_t *pmd; > spinlock_t *ptl; > int count = 0; > int i; > @@ -1509,12 +1520,7 @@ void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr) > } > > /* step 4: collapse pmd */ > - ptl = pmd_lock(vma->vm_mm, pmd); > - _pmd = pmdp_collapse_flush(vma, haddr, pmd); > - spin_unlock(ptl); > - mm_dec_nr_ptes(mm); > - pte_free(mm, pmd_pgtable(_pmd)); > - > + collapse_and_free_pmd(mm, vma, haddr, pmd); > drop_hpage: > unlock_page(hpage); > put_page(hpage); > @@ -1552,7 +1558,7 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff) > struct vm_area_struct *vma; > struct mm_struct *mm; > unsigned long addr; > - pmd_t *pmd, _pmd; > + pmd_t *pmd; > > i_mmap_lock_write(mapping); > vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) { > @@ -1591,14 +1597,8 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff) > * reverse order. Trylock is a way to avoid deadlock. > */ > if (mmap_write_trylock(mm)) { > - if (!khugepaged_test_exit(mm)) { > - spinlock_t *ptl = pmd_lock(mm, pmd); > - /* assume page table is clear */ > - _pmd = pmdp_collapse_flush(vma, addr, pmd); > - spin_unlock(ptl); > - mm_dec_nr_ptes(mm); > - pte_free(mm, pmd_pgtable(_pmd)); > - } > + if (!khugepaged_test_exit(mm)) > + collapse_and_free_pmd(mm, vma, addr, pmd); > mmap_write_unlock(mm); > } else { > /* Try again later */ > -- > 2.35.0.rc0.227.g00780c9af4-goog > >