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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1875EC433EF for ; Wed, 17 Nov 2021 19:49:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F0F9D613B5 for ; Wed, 17 Nov 2021 19:49:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240602AbhKQTwH (ORCPT ); Wed, 17 Nov 2021 14:52:07 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46178 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239106AbhKQTv7 (ORCPT ); Wed, 17 Nov 2021 14:51:59 -0500 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 C27A6C061764 for ; Wed, 17 Nov 2021 11:49:00 -0800 (PST) Received: by mail-yb1-xb4a.google.com with SMTP id u12-20020a25f80c000000b005dd97d128f7so5718326ybd.6 for ; Wed, 17 Nov 2021 11:49:00 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:message-id:mime-version:subject:from:to:cc; bh=PpBiG+58AqKHL1Onxjj1GmKlritKFJFCrusKbqqq2FE=; b=maTz4mTJBef5LXTAVKIznYcBVXrKhhbFl6Sjn9+9n+vlBMXlBUpILx8hnFowMWNKVR D5WvRhfmcQYN9632bBuUjcDJOx0Za+nMrkTvrkrULLFOWc2kOQ3RSu585cCQti/p2JWv UMg5QLlPEBP8hPnpQRW9cFEfW6yVss7tPH8vlStqQCRWpJAShgXCeKnibT1V8bMN4P2v RUYNNQvus91tdcZRcsUg/JgE6h0Z1Z9++YOloTZhtQaBPg01FDrZrzt+K/BB2qqxhye5 qD+NIdQfbgxdJPi8SqdTS8bVBGoHQdw+pchl5ktr/ug9I7tGRBmUWsLFGspntZ9ehaKW kODw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:message-id:mime-version:subject:from:to:cc; bh=PpBiG+58AqKHL1Onxjj1GmKlritKFJFCrusKbqqq2FE=; b=NziGla/AJYtsZxAmgVdHUYyCEZNXkCwlx+E7yVX0oI0aoZtwj0QrpMV02bO4GuoAqg FjL45Dnq5cpuvmN+kZ6VqHbxHeHz0qKqoNLR4mVjMvuAS7Zm1JgvsqHuCMyAClrOBkgM xT8vV5NqJYcH88QU/uwN5IYWfpYV1AUj8T3UXbY6ghBKe735bSvlkmQFzJ+BBvgiFBfL HSwwv3VL/FG755FwFHTplXJeTss+GmaA0i7XlLAmKgLsXHOT2a4VrCFArMnoKi1hlbK5 3ekJcm8nRF4a+6Wj0qm/gG5fxDuBFPLtHGaEh6wac9P9f/Kpuuxc7cEnxqUcHkGBEZDq s8jQ== X-Gm-Message-State: AOAM531j2iOBsFG+2K/UGpZAxD4hudhFukRrCWWHNTMkpiQJ6q+vFgud VWkKHZPSe0whwCO/lqh5EtTat/xMaeEqnOhdkw== X-Google-Smtp-Source: ABdhPJx/1FP76tKslX0j28CU2KgGpu+lsjLSgUFFLnvLWteC3/S8VHTgPQGZlFFscWKnSWSFZmyke9EFBaUr2IVJMA== X-Received: from almasrymina.svl.corp.google.com ([2620:15c:2cd:202:ab13:f492:fd91:a37d]) (user=almasrymina job=sendgmr) by 2002:a25:bfd2:: with SMTP id q18mr13117865ybm.542.1637178539930; Wed, 17 Nov 2021 11:48:59 -0800 (PST) Date: Wed, 17 Nov 2021 11:48:54 -0800 Message-Id: <20211117194855.398455-1-almasrymina@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.34.0.rc2.393.gf8c9666880-goog Subject: [PATCH v6] mm: Add PM_THP_MAPPED to /proc/pid/pagemap From: Mina Almasry To: Jonathan Corbet Cc: Mina Almasry , David Hildenbrand , Matthew Wilcox , "Paul E . McKenney" , Yu Zhao , Andrew Morton , Peter Xu , Ivan Teterevkov , Florian Schmidt , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-doc@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Add PM_THP_MAPPED MAPPING to allow userspace to detect whether a given virt address is currently mapped by a transparent huge page or not. Example use case is a process requesting THPs from the kernel (via a huge tmpfs mount for example), for a performance critical region of memory. The userspace may want to query whether the kernel is actually backing this memory by hugepages or not. PM_THP_MAPPED bit is set if the virt address is mapped at the PMD level and the underlying page is a transparent huge page. A few options were considered: 1. Add /proc/pid/pageflags that exports the same info as /proc/kpageflags. This is not appropriate because many kpageflags are inappropriate to expose to userspace processes. 2. Simply get this info from the existing /proc/pid/smaps interface. There are a couple of issues with that: 1. /proc/pid/smaps output is human readable and unfriendly to programatically parse. 2. /proc/pid/smaps is slow. The cost of reading /proc/pid/smaps into userspace buffers is about ~800us per call, and this doesn't include parsing the output to get the information you need. The cost of querying 1 virt address in /proc/pid/pagemaps however is around 5-7us. Tested manually by adding logging into transhuge-stress, and by allocating THP and querying the PM_THP_MAPPED flag at those virtual addresses. Signed-off-by: Mina Almasry Cc: David Hildenbrand Cc: Matthew Wilcox Cc: David Rientjes rientjes@google.com Cc: Paul E. McKenney Cc: Yu Zhao Cc: Jonathan Corbet Cc: Andrew Morton Cc: Peter Xu Cc: Ivan Teterevkov Cc: Florian Schmidt Cc: linux-kernel@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org Cc: linux-mm@kvack.org --- Changes in v6: - Renamed to PM_THP_MAPPED - Removed changes to transhuge-stress Changes in v5: - Added justification for this interface in the commit message! Changes in v4: - Removed unnecessary moving of flags variable declaration Changes in v3: - Renamed PM_THP to PM_HUGE_THP_MAPPING - Fixed checks to set PM_HUGE_THP_MAPPING - Added PM_HUGE_THP_MAPPING docs --- Documentation/admin-guide/mm/pagemap.rst | 3 ++- fs/proc/task_mmu.c | 3 +++ 2 files changed, 5 insertions(+), 1 deletion(-) diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst index fdc19fbc10839..8a0f0064ff336 100644 --- a/Documentation/admin-guide/mm/pagemap.rst +++ b/Documentation/admin-guide/mm/pagemap.rst @@ -23,7 +23,8 @@ There are four components to pagemap: * Bit 56 page exclusively mapped (since 4.2) * Bit 57 pte is uffd-wp write-protected (since 5.13) (see :ref:`Documentation/admin-guide/mm/userfaultfd.rst `) - * Bits 57-60 zero + * Bit 58 page is a huge (PMD size) THP mapping + * Bits 59-60 zero * Bit 61 page is file-page or shared-anon (since 3.5) * Bit 62 page swapped * Bit 63 page present diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index ad667dbc96f5c..d784a97aa209a 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -1302,6 +1302,7 @@ struct pagemapread { #define PM_SOFT_DIRTY BIT_ULL(55) #define PM_MMAP_EXCLUSIVE BIT_ULL(56) #define PM_UFFD_WP BIT_ULL(57) +#define PM_THP_MAPPED BIT_ULL(58) #define PM_FILE BIT_ULL(61) #define PM_SWAP BIT_ULL(62) #define PM_PRESENT BIT_ULL(63) @@ -1456,6 +1457,8 @@ static int pagemap_pmd_range(pmd_t *pmdp, unsigned long addr, unsigned long end, if (page && page_mapcount(page) == 1) flags |= PM_MMAP_EXCLUSIVE; + if (page && is_transparent_hugepage(page)) + flags |= PM_THP_MAPPED; for (; addr != end; addr += PAGE_SIZE) { pagemap_entry_t pme = make_pme(frame, flags); -- 2.34.0.rc2.393.gf8c9666880-goog