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Sat, 13 Jul 2024 02:25:40 -0700 (PDT) X-Google-Smtp-Source: AGHT+IEep5nCRORM9rbDk8yQvtZf8RFQzchFGR+rMgXtq0XU0SPUCCZHwDTSqxwRfdSOKgopRMqybg== X-Received: by 2002:a05:6a20:394a:b0:1be:c43c:e1cc with SMTP id adf61e73a8af0-1c2980f9522mr16226553637.10.1720862740148; Sat, 13 Jul 2024 02:25:40 -0700 (PDT) Received: from [192.168.68.54] ([43.252.112.134]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-1fc0bb6fec6sm6940235ad.27.2024.07.13.02.25.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 13 Jul 2024 02:25:39 -0700 (PDT) Message-ID: Date: Sat, 13 Jul 2024 19:25:34 +1000 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: David Hildenbrand , 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> Content-Language: en-US From: Gavin Shan In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 7/13/24 11:03 AM, David Hildenbrand wrote: > On 12.07.24 07:39, Gavin Shan wrote: >> >> 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 > Ok. It will be corrected in v2. >> +#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. > Sure, it will be removed in v2. >>    /* >>     * 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? > With previous fixes and this one, I don't see there is any missed cases for shmem to have 512MB page cache, exceeding MAX_PAGECACHE_ORDER. Hopefully, I don't miss anything from the code inspection. - regular read/write paths: covered by the previous fixes - synchronous readahead: covered by the previous fixes - asynchronous readahead: page size granularity, no huge page - page fault handling: covered by the previous fixes - collapsing PTEs to PMD: to be covered by this patch - swapin: shouldn't have 512MB huge page since we don't have such huge pages during swapout period - other cases I missed (?) Thanks, Gavin