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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8C030E732C5 for ; Thu, 28 Sep 2023 11:59:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232029AbjI1L7t (ORCPT ); Thu, 28 Sep 2023 07:59:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39724 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229980AbjI1L7s (ORCPT ); Thu, 28 Sep 2023 07:59:48 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 9DA0A121; Thu, 28 Sep 2023 04:59:46 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A25D51FB; Thu, 28 Sep 2023 05:00:24 -0700 (PDT) Received: from [10.1.37.161] (XHFQ2J9959.cambridge.arm.com [10.1.37.161]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id EF6F23F5A1; Thu, 28 Sep 2023 04:59:44 -0700 (PDT) Message-ID: <54e5accf-1a56-495a-a4f5-d57504bc2fc8@arm.com> Date: Thu, 28 Sep 2023 12:59:43 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: BUG: MADV_COLLAPSE doesn't work for XFS files Content-Language: en-GB To: Bagas Sanjaya , Hugh Dickins , David Hildenbrand , Matthew Wilcox , zokeefe@google.com, Chandan Babu R , "Darrick J. Wong" Cc: Linux Memory Management List , Linux XFS , Linux Kernel Mailing List References: <4d6c9b19-cdbb-4a00-9a40-5ed5c36332e5@arm.com> From: Ryan Roberts In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On 28/09/2023 11:54, Bagas Sanjaya wrote: > On Thu, Sep 28, 2023 at 10:55:17AM +0100, Ryan Roberts wrote: >> Hi all, >> >> I've just noticed that when applied to a file mapping for a file on xfs, MADV_COLLAPSE returns EINVAL. The same test case works fine if the file is on ext4. >> >> I think the root cause is that the implementation bails out if it finds a (non-PMD-sized) large folio in the page cache for any part of the file covered by the region. XFS does readahead into large folios so we hit this issue. See khugepaged.h:collapse_file(): >> >> if (PageTransCompound(page)) { >> struct page *head = compound_head(page); >> >> result = compound_order(head) == HPAGE_PMD_ORDER && >> head->index == start >> /* Maybe PMD-mapped */ >> ? SCAN_PTE_MAPPED_HUGEPAGE >> : SCAN_PAGE_COMPOUND; >> goto out_unlock; >> } > > I don't see any hint to -EINVAL above. Am I missing something? The SCAN_PAGE_COMPOUND result ends up back at madvise_collapse() where it eventually gets converted to -EINVAL by madvise_collapse_errno(). > >> >> I'm not sure if this is already a known issue? I don't have time to work on a fix for this right now, so thought I would highlight it at least. I might get around to it at some point in the future if nobody else tackles it. >> >> Thanks, >> Ryan >> >> >> Test case I've been using: >> >> -->8-- >> >> #include >> #include >> #include >> #include >> #include >> #include >> #include >> >> #ifndef MADV_COLLAPSE >> #define MADV_COLLAPSE 25 >> #endif >> >> #define handle_error(msg) do { perror(msg); exit(EXIT_FAILURE); } while (0) >> >> #define SZ_1K 1024 >> #define SZ_1M (SZ_1K * SZ_1K) >> #define ALIGN(val, align) (((val) + ((align) - 1)) & ~((align) - 1)) >> >> #if 1 >> // ext4 >> #define DATA_FILE "/home/ubuntu/data.txt" >> #else >> // xfs >> #define DATA_FILE "/boot/data.txt" >> #endif >> >> int main(void) >> { >> int fd; >> char *mem; >> int ret; >> >> fd = open(DATA_FILE, O_RDONLY); >> if (fd == -1) >> handle_error("open"); >> >> mem = mmap(NULL, SZ_1M * 4, PROT_READ | PROT_EXEC, MAP_PRIVATE, fd, 0); >> close(fd); >> if (mem == MAP_FAILED) >> handle_error("mmap"); >> >> printf("1: pid=%d, mem=%p\n", getpid(), mem); >> getchar(); >> >> mem = (char *)ALIGN((unsigned long)mem, SZ_1M * 2); >> ret = madvise(mem, SZ_1M * 2, MADV_COLLAPSE); >> if (ret) >> handle_error("madvise"); >> >> printf("2: pid=%d, mem=%p\n", getpid(), mem); >> getchar(); >> >> return 0; >> } >> >> -->8-- >> > > Confused... This is a user space test case that shows the problem; data.txt needs to be at least 4MB and on a mounted ext4 and xfs filesystem. By toggling the '#if 1' to 0, you can see the different behaviours for ext4 and xfs - handle_error("madvise") fires with EINVAL in the xfs case. The getchar()s are leftovers from me looking at the smaps file. >