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Message-ID: <9cb900f1-6b49-4160-adc2-cdeae1b00b17@huawei.com>
Date: Wed, 8 Nov 2023 09:41:32 +0800
From: Kefeng Wang <wangkefeng.wang@...wei.com>
To: Sidhartha Kumar <sidhartha.kumar@...cle.com>,
Andrew Morton <akpm@...ux-foundation.org>
CC: <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
Matthew Wilcox <willy@...radead.org>,
David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH 4/6] mm: memory: use a folio in do_cow_page()
On 2023/11/8 2:27, Sidhartha Kumar wrote:
> On 11/7/23 5:52 AM, Kefeng Wang wrote:
>> Use folio_prealloc() helper and convert to use a folio in
>> do_cow_page(), which save five compound_head() calls.
>>
>> Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
>> ---
>> mm/memory.c | 16 ++++++----------
>> 1 file changed, 6 insertions(+), 10 deletions(-)
>>
>> diff --git a/mm/memory.c b/mm/memory.c
>> index 062136d25da3..5ecee3eac29d 100644
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -4648,6 +4648,7 @@ static vm_fault_t do_read_fault(struct vm_fault
>> *vmf)
>> static vm_fault_t do_cow_fault(struct vm_fault *vmf)
>> {
>> struct vm_area_struct *vma = vmf->vma;
>> + struct folio *folio;
>> vm_fault_t ret;
>> ret = vmf_can_call_fault(vmf);
>> @@ -4656,16 +4657,11 @@ static vm_fault_t do_cow_fault(struct vm_fault
>> *vmf)
>> if (ret)
>> return ret;
>> - vmf->cow_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma,
>> vmf->address);
>> - if (!vmf->cow_page)
>> + folio = folio_prealloc(vma->vm_mm, vma, vmf->address, false);
>> + if (!folio)
>> return VM_FAULT_OOM;
>> - if (mem_cgroup_charge(page_folio(vmf->cow_page), vma->vm_mm,
>> - GFP_KERNEL)) {
>> - put_page(vmf->cow_page);
>> - return VM_FAULT_OOM;
>> - }
>> - folio_throttle_swaprate(page_folio(vmf->cow_page), GFP_KERNEL);
>
> Hi Kefeng,
>
> I was wondering why this block of code is no longer needed after using a
> folio?
folio_prealloc(previous page_copy_prealloc) already with above code.
>
> Thanks,
> Sidhartha Kumar
>
>> + vmf->cow_page = &folio->page;
>> ret = __do_fault(vmf);
>> if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE |
>> VM_FAULT_RETRY)))
>> @@ -4674,7 +4670,7 @@ static vm_fault_t do_cow_fault(struct vm_fault
>> *vmf)
>> return ret;
>> copy_user_highpage(vmf->cow_page, vmf->page, vmf->address, vma);
>> - __SetPageUptodate(vmf->cow_page);
>> + __folio_mark_uptodate(folio);
>> ret |= finish_fault(vmf);
>> unlock_page(vmf->page);
>> @@ -4683,7 +4679,7 @@ static vm_fault_t do_cow_fault(struct vm_fault
>> *vmf)
>> goto uncharge_out;
>> return ret;
>> uncharge_out:
>> - put_page(vmf->cow_page);
>> + folio_put(folio);
>> return ret;
>> }
>
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