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Fri, 12 Jul 2024 18:03:11 -0700 (PDT) X-Google-Smtp-Source: AGHT+IFwvIyu645ginLcnOU79cuOOkLvO6pcECrChF26Gh5N2PEpynwczfyA7mKSNLq2ec+lPeS1Mg== X-Received: by 2002:a17:902:e54e:b0:1fb:9cb0:3e46 with SMTP id d9443c01a7336-1fc0b4b6453mr4689775ad.7.1720832591455; Fri, 12 Jul 2024 18:03:11 -0700 (PDT) Received: from [172.20.2.228] ([4.28.11.157]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-1fc0bb6ffdesm597715ad.53.2024.07.12.18.03.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 12 Jul 2024 18:03:11 -0700 (PDT) Message-ID: Date: Sat, 13 Jul 2024 03:03:10 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/huge_memory: Avoid PMD-size page cache if needed To: Gavin Shan , Matthew Wilcox Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, william.kucharski@oracle.com, ryan.roberts@arm.com, shan.gavin@gmail.com References: <20240711104840.200573-1-gshan@redhat.com> <63a0364b-a2e0-48c2-b255-e976112deeb1@redhat.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 12.07.24 07:39, Gavin Shan wrote: > On 7/12/24 7:03 AM, David Hildenbrand wrote: >> On 11.07.24 22:46, Matthew Wilcox wrote: >>> On Thu, Jul 11, 2024 at 08:48:40PM +1000, Gavin Shan wrote: >>>> +++ b/mm/huge_memory.c >>>> @@ -136,7 +136,8 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma, >>>>           while (orders) { >>>>               addr = vma->vm_end - (PAGE_SIZE << order); >>>> -            if (thp_vma_suitable_order(vma, addr, order)) >>>> +            if (!(vma->vm_file && order > MAX_PAGECACHE_ORDER) && >>>> +                thp_vma_suitable_order(vma, addr, order)) >>>>                   break; >>> >>> Why does 'orders' even contain potential orders that are larger than >>> MAX_PAGECACHE_ORDER? >>> >>> We do this at the top: >>> >>>          orders &= vma_is_anonymous(vma) ? >>>                          THP_ORDERS_ALL_ANON : THP_ORDERS_ALL_FILE; >>> >>> include/linux/huge_mm.h:#define THP_ORDERS_ALL_FILE     (BIT(PMD_ORDER) | BIT(PUD_ORDER)) >>> >>> ... and that seems very wrong.  We support all kinds of orders for >>> files, not just PMD order.  We don't support PUD order at all. >>> >>> What the hell is going on here? >> >> yes, that's just absolutely confusing. I mentioned it to Ryan lately that we should clean that up (I wanted to look into that, but am happy if someone else can help). >> >> There should likely be different defines for >> >> DAX (PMD|PUD) >> >> SHMEM (PMD) -- but soon more. Not sure if we want separate ANON_SHMEM for the time being. Hm. But shmem is already handles separately, so maybe we can just ignore shmem here. >> >> PAGECACHE (1 .. MAX_PAGECACHE_ORDER) >> >> ? But it's still unclear to me. >> >> At least DAX must stay special I think, and PAGECACHE should be capped at MAX_PAGECACHE_ORDER. >> > > David, I can help to clean it up. Could you please help to confirm the following Thanks! > changes are exactly what you're suggesting? Hopefully, there are nothing I've missed. > The original issue can be fixed by the changes. With the changes applied, madvise(MADV_COLLAPSE) > returns with errno -22 in the test program. > > The fix tag needs to adjusted either. > > Fixes: 3485b88390b0 ("mm: thp: introduce multi-size THP sysfs interface") > > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h > index 2aa986a5cd1b..45909efb0ef0 100644 > --- a/include/linux/huge_mm.h > +++ b/include/linux/huge_mm.h > @@ -74,7 +74,12 @@ extern struct kobj_attribute shmem_enabled_attr; > /* > * Mask of all large folio orders supported for file THP. > */ > -#define THP_ORDERS_ALL_FILE (BIT(PMD_ORDER) | BIT(PUD_ORDER)) DAX doesn't have any MAX_PAGECACHE_ORDER restrictions (like hugetlb). So this should be /* * FSDAX never splits folios, so the MAX_PAGECACHE_ORDER limit does not * apply here. */ THP_ORDERS_ALL_FILE_DAX ((BIT(PMD_ORDER) | BIT(PUD_ORDER)) Something like that > +#define THP_ORDERS_ALL_FILE_DAX \ > + ((BIT(PMD_ORDER) | BIT(PUD_ORDER)) & (BIT(MAX_PAGECACHE_ORDER + 1) - 1)) > +#define THP_ORDERS_ALL_FILE_DEFAULT \ > + ((BIT(MAX_PAGECACHE_ORDER + 1) - 1) & ~BIT(0)) > +#define THP_ORDERS_ALL_FILE \ > + (THP_ORDERS_ALL_FILE_DAX | THP_ORDERS_ALL_FILE_DEFAULT) Maybe we can get rid of THP_ORDERS_ALL_FILE (to prevent abuse) and fixup THP_ORDERS_ALL instead. > > /* > * Mask of all large folio orders supported for THP. > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 2120f7478e55..4690f33afaa6 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -88,9 +88,17 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma, > bool smaps = tva_flags & TVA_SMAPS; > bool in_pf = tva_flags & TVA_IN_PF; > bool enforce_sysfs = tva_flags & TVA_ENFORCE_SYSFS; > + unsigned long supported_orders; > + > /* Check the intersection of requested and supported orders. */ > - orders &= vma_is_anonymous(vma) ? > - THP_ORDERS_ALL_ANON : THP_ORDERS_ALL_FILE; > + if (vma_is_anonymous(vma)) > + supported_orders = THP_ORDERS_ALL_ANON; > + else if (vma_is_dax(vma)) > + supported_orders = THP_ORDERS_ALL_FILE_DAX; > + else > + supported_orders = THP_ORDERS_ALL_FILE_DEFAULT; This is what I had in mind. But, do we have to special-case shmem as well or will that be handled correctly? -- Cheers, David / dhildenb