From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf1-f199.google.com (mail-pf1-f199.google.com [209.85.210.199]) by kanga.kvack.org (Postfix) with ESMTP id EA79E6B000D for ; Thu, 18 Oct 2018 23:50:26 -0400 (EDT) Received: by mail-pf1-f199.google.com with SMTP id g63-v6so15182673pfc.9 for ; Thu, 18 Oct 2018 20:50:26 -0700 (PDT) Received: from ipmail03.adl2.internode.on.net (ipmail03.adl2.internode.on.net. [150.101.137.141]) by mx.google.com with ESMTP id z67-v6si16874380pfz.5.2018.10.18.20.50.25 for ; Thu, 18 Oct 2018 20:50:25 -0700 (PDT) Date: Fri, 19 Oct 2018 14:27:22 +1100 From: Dave Chinner Subject: Re: [PATCH 4/7] mm: use the cached page for filemap_fault Message-ID: <20181019032722.GJ18822@dastard> References: <20181018202318.9131-1-josef@toxicpanda.com> <20181018202318.9131-5-josef@toxicpanda.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181018202318.9131-5-josef@toxicpanda.com> Sender: owner-linux-mm@kvack.org List-ID: To: Josef Bacik Cc: kernel-team@fb.com, hannes@cmpxchg.org, linux-kernel@vger.kernel.org, tj@kernel.org, akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-btrfs@vger.kernel.org, riel@fb.com, linux-mm@kvack.org On Thu, Oct 18, 2018 at 04:23:15PM -0400, Josef Bacik wrote: > If we drop the mmap_sem we have to redo the vma lookup which requires > redoing the fault handler. Chances are we will just come back to the > same page, so save this page in our vmf->cached_page and reuse it in the > next loop through the fault handler. > > Signed-off-by: Josef Bacik > --- > mm/filemap.c | 30 ++++++++++++++++++++++++++++-- > 1 file changed, 28 insertions(+), 2 deletions(-) > > diff --git a/mm/filemap.c b/mm/filemap.c > index 65395ee132a0..5212ab637832 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -2530,13 +2530,38 @@ vm_fault_t filemap_fault(struct vm_fault *vmf) > pgoff_t offset = vmf->pgoff; > int flags = vmf->flags; > pgoff_t max_off; > - struct page *page; > + struct page *page = NULL; > + struct page *cached_page = vmf->cached_page; > vm_fault_t ret = 0; > > max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE); > if (unlikely(offset >= max_off)) > return VM_FAULT_SIGBUS; > > + /* > + * We may have read in the page already and have a page from an earlier > + * loop. If so we need to see if this page is still valid, and if not > + * do the whole dance over again. > + */ > + if (cached_page) { > + if (flags & FAULT_FLAG_KILLABLE) { > + error = lock_page_killable(cached_page); > + if (error) { > + up_read(&mm->mmap_sem); > + goto out_retry; > + } > + } else > + lock_page(cached_page); > + vmf->cached_page = NULL; > + if (cached_page->mapping == mapping && > + cached_page->index == offset) { > + page = cached_page; > + goto have_cached_page; > + } > + unlock_page(cached_page); > + put_page(cached_page); > + } > + Can you factor this out so the main code path doesn't get any more complex than it already is? i.e. something like: error = vmf_has_cached_page(vmf, &page); if (error) goto out_retry; if (page) goto have_cached_page; -dave. -- Dave Chinner david@fromorbit.com