From nobody Sun Feb 8 13:53:27 2026 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 78A61C7EE23 for ; Mon, 15 May 2023 17:28:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244153AbjEOR2w (ORCPT ); Mon, 15 May 2023 13:28:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49082 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244288AbjEOR1l (ORCPT ); Mon, 15 May 2023 13:27:41 -0400 Received: from mail-yb1-xb4a.google.com (mail-yb1-xb4a.google.com [IPv6:2607:f8b0:4864:20::b4a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A492214342 for ; Mon, 15 May 2023 10:26:26 -0700 (PDT) Received: by mail-yb1-xb4a.google.com with SMTP id 3f1490d57ef6-ba7831dfe95so4179676276.2 for ; Mon, 15 May 2023 10:26:26 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1684171584; x=1686763584; h=cc:to:from:subject:message-id:mime-version:date:from:to:cc:subject :date:message-id:reply-to; bh=y97BQ7sR2LBYQN45EWEO4FJ6RSEUfFrbQxSXtC1eEEg=; b=lnrHEXI214x0JOHTaG19NvuKmqNZq8vfQFKdpU6IFL5CrGuJIGS18GJfVi7BwsHwLu z/19S9vAZW30pNF09qix5IlZ31ZEXIfoGPrblHX6Enf6KFUoXTTZnWap+ULYaVY8vhtU OkCdhS24qIkQeup6yuRZj7uh7CWNtThe5UGcraCNGfBBC5Hww348MxDxRagpAxcDVTgA AZ7h+zuAXJzQAH2BNFM6Zv0fa/yUNkqKLh+ZXEOhgjyLaqTiXJhjvNH8l0R1RPrqwNd7 0RKoPgChapU4TerGr+ESr+HQzkCOntbXEi2Aj+4c6i7PG4f7i/oYDqbdgA2BE8qDfgLN /7wQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1684171584; x=1686763584; h=cc:to:from:subject:message-id:mime-version:date:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=y97BQ7sR2LBYQN45EWEO4FJ6RSEUfFrbQxSXtC1eEEg=; b=CdBiaWx1LxX3ezy+P4iV4RdOeOG7o8BYzmmSVmxcCey7i+JFbiqfwvPOSBffudXmG/ F6BSiiGGVmGZF2e+FY+mI2qHvLISEkE24OJN386WcpXNGf8kWn/69m2Jv599hopJe9yh CTqmS3sQWkdIsICdxHoidpbaRIVlg68jqdIuKqvGKEXXTfmsNgQR16muNWUtCMkpD0R9 n6vFrv3oE+9vddW/J47MZTuiJYxcf93BvWP7DDNxEpfARklKJUuiubm7iDehOaH9y0f/ D1tH9C37zFsPQ66N47lovLFd4PFSRhmznIdGUn3oaaoyfYCgUmjJ+1wLWRVSGASwJOAk Cpcw== X-Gm-Message-State: AC+VfDyS6QIXUKfBZCMOWnjP5lDttwvp+ZVbDY5N9wezD8q+Nt26wICl 9Mc5U9H1OvO/niyoHIamZYoMvJB+Rh/q X-Google-Smtp-Source: ACHHUZ5TeR03DncbFn2MDJZP9KzUWVPcJVpfEqM7CUznGNTSHd5/NHOxIZ8GKK9NiQzFZ/fPDVHY/iZDWiai X-Received: from yuanchu.bej.corp.google.com ([2401:fa00:44:10:166c:6ee8:fb91:4744]) (user=yuanchu job=sendgmr) by 2002:a5b:750:0:b0:ba7:75a8:e37d with SMTP id s16-20020a5b0750000000b00ba775a8e37dmr3199880ybq.4.1684171584365; Mon, 15 May 2023 10:26:24 -0700 (PDT) Date: Tue, 16 May 2023 01:26:08 +0800 Mime-Version: 1.0 X-Mailer: git-send-email 2.40.1.606.ga4b1b128d6-goog Message-ID: <20230515172608.3558391-1-yuanchu@google.com> Subject: [PATCH] mm: pagemap: restrict pagewalk to the requested range From: Yuanchu Xie To: Andrew Morton Cc: "Liam R . Howlett" , Yang Shi , "Zach O'Keefe" , Peter Xu , "Kirill A . Shutemov" , Matthew Wilcox , Pasha Tatashin , Yuanchu Xie , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The pagewalk in pagemap_read reads one PTE past the end of the requested range, and stops when the buffer runs out of space. While it produces the right result, the extra read is unnecessary and less performant. I timed the following command before and after this patch: dd count=3D100000 if=3D/proc/self/pagemap of=3D/dev/null The results are consistently within 0.001s across 5 runs. Before: 100000+0 records in 100000+0 records out 51200000 bytes (51 MB) copied, 0.0763159 s, 671 MB/s real 0m0.078s user 0m0.012s sys 0m0.065s After: 100000+0 records in 100000+0 records out 51200000 bytes (51 MB) copied, 0.0487928 s, 1.0 GB/s real 0m0.050s user 0m0.011s sys 0m0.039s Signed-off-by: Yuanchu Xie Acked-by: David Rientjes Acked-by: Mike Rapoport (IBM) Acked-by: Peter Xu Reviewed-by: Yang Shi --- fs/proc/task_mmu.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index 420510f6a545..6259dd432eeb 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -1689,23 +1689,23 @@ static ssize_t pagemap_read(struct file *file, char= __user *buf, /* watch out for wraparound */ start_vaddr =3D end_vaddr; if (svpfn <=3D (ULONG_MAX >> PAGE_SHIFT)) { + unsigned long end; + ret =3D mmap_read_lock_killable(mm); if (ret) goto out_free; start_vaddr =3D untagged_addr_remote(mm, svpfn << PAGE_SHIFT); mmap_read_unlock(mm); + + end =3D start_vaddr + ((count / PM_ENTRY_BYTES) << PAGE_SHIFT); + if (end >=3D start_vaddr && end < mm->task_size) + end_vaddr =3D end; } =20 /* Ensure the address is inside the task */ if (start_vaddr > mm->task_size) start_vaddr =3D end_vaddr; =20 - /* - * The odds are that this will stop walking way - * before end_vaddr, because the length of the - * user buffer is tracked in "pm", and the walk - * will stop when we hit the end of the buffer. - */ ret =3D 0; while (count && (start_vaddr < end_vaddr)) { int len; --=20 2.40.1.606.ga4b1b128d6-goog