From: Dave Chinner <david@fromorbit.com>
To: Josef Bacik <josef@toxicpanda.com>
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
Subject: Re: [PATCH 4/7] mm: use the cached page for filemap_fault
Date: Fri, 19 Oct 2018 14:27:22 +1100 [thread overview]
Message-ID: <20181019032722.GJ18822@dastard> (raw)
In-Reply-To: <20181018202318.9131-5-josef@toxicpanda.com>
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 <josef@toxicpanda.com>
> ---
> 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
next prev parent reply other threads:[~2018-10-19 3:50 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-18 20:23 [PATCH 0/7][V3] drop the mmap_sem when doing IO in the fault path Josef Bacik
2018-10-18 20:23 ` [PATCH 1/7] mm: infrastructure for page fault page caching Josef Bacik
2018-10-18 20:23 ` [PATCH 2/7] mm: drop mmap_sem for page cache read IO submission Josef Bacik
2018-10-19 3:14 ` Dave Chinner
2018-10-18 20:23 ` [PATCH 3/7] mm: drop the mmap_sem in all read fault cases Josef Bacik
2018-10-19 3:21 ` Dave Chinner
2018-10-18 20:23 ` [PATCH 4/7] mm: use the cached page for filemap_fault Josef Bacik
2018-10-19 3:27 ` Dave Chinner [this message]
2018-10-18 20:23 ` [PATCH 5/7] mm: add a flag to indicate we used a cached page Josef Bacik
2018-10-19 3:34 ` Dave Chinner
2018-10-18 20:23 ` [PATCH 6/7] mm: allow ->page_mkwrite to do retries Josef Bacik
2018-10-19 3:36 ` Dave Chinner
2018-10-18 20:23 ` [PATCH 7/7] btrfs: drop mmap_sem in mkwrite for btrfs Josef Bacik
2018-10-19 3:48 ` Dave Chinner
2018-10-22 17:56 ` Josef Bacik
2018-10-22 21:31 ` Dave Chinner
2018-10-25 13:22 ` Jan Kara
2018-10-25 13:58 ` Josef Bacik
2018-10-26 9:47 ` Jan Kara
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