From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f70.google.com (mail-lf0-f70.google.com [209.85.215.70]) by kanga.kvack.org (Postfix) with ESMTP id 6FCFD6B02A1 for ; Wed, 2 Nov 2016 03:37:23 -0400 (EDT) Received: by mail-lf0-f70.google.com with SMTP id o141so1517282lff.7 for ; Wed, 02 Nov 2016 00:37:23 -0700 (PDT) Received: from mail-lf0-x241.google.com (mail-lf0-x241.google.com. [2a00:1450:4010:c07::241]) by mx.google.com with ESMTPS id z131si490403lfa.326.2016.11.02.00.37.21 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 02 Nov 2016 00:37:21 -0700 (PDT) Received: by mail-lf0-x241.google.com with SMTP id i187so458078lfe.1 for ; Wed, 02 Nov 2016 00:37:21 -0700 (PDT) Date: Wed, 2 Nov 2016 10:31:57 +0300 From: "Kirill A. Shutemov" Subject: Re: [PATCH 2/2] mm: add PageWaiters bit to indicate waitqueue should be checked Message-ID: <20161102073156.GA13949@node.shutemov.name> References: <20161102070346.12489-1-npiggin@gmail.com> <20161102070346.12489-3-npiggin@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161102070346.12489-3-npiggin@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: Nicholas Piggin Cc: linux-mm , Andrew Morton , "Kirill A. Shutemov" , Johannes Weiner , Jan Kara , Mel Gorman , Peter Zijlstra , Rik van Riel , Linus Torvalds , Hugh Dickins On Wed, Nov 02, 2016 at 06:03:46PM +1100, Nicholas Piggin wrote: > Add a new page flag, PageWaiters. This bit is always set when the > page has waiters on page_waitqueue(page), within the same synchronization > scope as waitqueue_active(page) (i.e., it is manipulated under waitqueue > lock). It may be set in some cases where that condition is not true > (e.g., some scenarios of hash collisions or signals waking page waiters). > > This bit can be used to avoid the costly waitqueue_active test for most > cases where the page has no waiters (the hashed address effectively adds > another line of cache footprint for most page operations). In cases where > the bit is set when the page has no waiters, the slower wakeup path will > end up clearing up the bit. > > The generic bit-waitqueue infrastructure is no longer used for pages, and > instead waitqueues are used directly with a custom key type. The generic > code was not flexible enough to do PageWaiters manipulation under waitqueue > lock, or always allow danging bits to be cleared when no waiters for this > page on the waitqueue. > > The upshot is that the page wait is much more flexible now, and could be > easily extended to wait on other properties of the page (by carrying that > data in the wait key). > > This improves the performance of a streaming write into a preallocated > tmpfs file by 2.2% on a POWER8 system with 64K pages (which is pretty > significant if there is only a single unlock_page per 64K of copy_from_user). > > Idea seems to have been around for a while, https://lwn.net/Articles/233391/ > > --- > include/linux/page-flags.h | 2 + > include/linux/pagemap.h | 23 +++--- > include/trace/events/mmflags.h | 1 + > mm/filemap.c | 157 ++++++++++++++++++++++++++++++++--------- > mm/swap.c | 2 + > 5 files changed, 138 insertions(+), 47 deletions(-) > > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > index 58d30b8..da40a1d 100644 > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -73,6 +73,7 @@ > */ > enum pageflags { > PG_locked, /* Page is locked. Don't touch. */ > + PG_waiters, /* Page has waiters, check its waitqueue */ > PG_error, > PG_referenced, > PG_uptodate, > @@ -255,6 +256,7 @@ static inline int TestClearPage##uname(struct page *page) { return 0; } > TESTSETFLAG_FALSE(uname) TESTCLEARFLAG_FALSE(uname) > > __PAGEFLAG(Locked, locked, PF_NO_TAIL) > +PAGEFLAG(Waiters, waiters, PF_NO_COMPOUND) __CLEARPAGEFLAG(Waiters, waiters, PF_NO_COMPOUND) This should be at least PF_NO_TAIL to work with shmem/tmpfs huge pages. -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org