From: Jan Kara <jack@suse.cz>
To: Josef Bacik <josef@toxicpanda.com>
Cc: kernel-team@fb.com, hannes@cmpxchg.org,
linux-kernel@vger.kernel.org, tj@kernel.org, david@fromorbit.com,
akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org,
linux-mm@kvack.org, riel@redhat.com, jack@suse.cz
Subject: Re: [PATCH 2/4] filemap: kill page_cache_read usage in filemap_fault
Date: Fri, 7 Dec 2018 10:57:50 +0100 [thread overview]
Message-ID: <20181207095750.GC13008@quack2.suse.cz> (raw)
In-Reply-To: <20181130195812.19536-3-josef@toxicpanda.com>
On Fri 30-11-18 14:58:10, Josef Bacik wrote:
> If we do not have a page at filemap_fault time we'll do this weird
> forced page_cache_read thing to populate the page, and then drop it
> again and loop around and find it. This makes for 2 ways we can read a
> page in filemap_fault, and it's not really needed. Instead add a
> FGP_FOR_MMAP flag so that pagecache_get_page() will return a unlocked
> page that's in pagecache. Then use the normal page locking and readpage
> logic already in filemap_fault. This simplifies the no page in page
> cache case significantly.
>
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Thanks for the patch. I like the simplification but I think it could be
even improved... see below.
> @@ -2449,9 +2426,11 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
> count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT);
> ret = VM_FAULT_MAJOR;
> retry_find:
> - page = find_get_page(mapping, offset);
> + page = pagecache_get_page(mapping, offset,
> + FGP_CREAT|FGP_FOR_MMAP,
> + vmf->gfp_mask);
> if (!page)
> - goto no_cached_page;
> + return vmf_error(-ENOMEM);
So why don't you just do:
page = pagecache_get_page(mapping, offset,
FGP_CREAT | FGP_LOCK, vmf->gfp_mask);
if (!page)
return vmf_error(-ENOMEM);
goto check_uptodate;
where check_uptodate would be a label before 'PageUptodate' check?
Then you don't have to introduce new flag for pagecache_get_page() and you
also don't have to unlock and then lock again the page... And you can still
delete all the code you've deleted.
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2018-12-07 9:57 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-30 19:58 [PATCH 0/4][V4] drop the mmap_sem when doing IO in the fault path Josef Bacik
2018-11-30 19:58 ` [PATCH 1/4] mm: infrastructure for page fault page caching Josef Bacik
2018-12-04 22:49 ` Andrew Morton
2018-11-30 19:58 ` [PATCH 2/4] filemap: kill page_cache_read usage in filemap_fault Josef Bacik
2018-12-05 21:52 ` Johannes Weiner
2018-12-07 9:57 ` Jan Kara [this message]
2018-12-07 10:37 ` Jan Kara
2018-11-30 19:58 ` [PATCH 3/4] filemap: drop the mmap_sem for all blocking operations Josef Bacik
2018-12-04 22:50 ` Andrew Morton
2018-12-05 22:23 ` Johannes Weiner
2018-12-07 11:01 ` Jan Kara
2018-12-10 18:44 ` Josef Bacik
2018-12-11 9:40 ` Jan Kara
2018-12-11 16:08 ` Josef Bacik
2018-12-11 16:38 ` Jan Kara
2018-11-30 19:58 ` [PATCH 4/4] mm: use the cached page for filemap_fault Josef Bacik
2018-12-04 22:50 ` Andrew Morton
2018-12-05 14:58 ` Josef Bacik
2018-12-07 11:03 ` Jan Kara
2018-12-04 22:49 ` [PATCH 0/4][V4] drop the mmap_sem when doing IO in the fault path Andrew Morton
2018-12-06 22:24 ` Dave Chinner
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