From: Eric Biggers <ebiggers@kernel.org>
To: Vyacheslav Dubeyko <slava@dubeyko.com>
Cc: linux-fscrypt@vger.kernel.org, linux-ext4@vger.kernel.org,
linux-f2fs-devel@lists.sourceforge.net,
linux-fsdevel@vger.kernel.org,
Victor Hsieh <victorhsieh@google.com>
Subject: Re: [PATCH] fs-verity: implement readahead for FS_IOC_ENABLE_VERITY
Date: Wed, 4 Dec 2019 10:10:56 -0800 [thread overview]
Message-ID: <20191204181056.GA4576@sol.localdomain> (raw)
In-Reply-To: <96a288281d9d84f11dcc06e62a1ff20e2bb2f776.camel@dubeyko.com>
On Wed, Dec 04, 2019 at 10:53:50AM +0300, Vyacheslav Dubeyko wrote:
> > diff --git a/fs/verity/enable.c b/fs/verity/enable.c
> > index eabc6ac19906..f7eaffa60196 100644
> > --- a/fs/verity/enable.c
> > +++ b/fs/verity/enable.c
> > @@ -13,14 +13,44 @@
> > #include <linux/sched/signal.h>
> > #include <linux/uaccess.h>
> >
> > -static int build_merkle_tree_level(struct inode *inode, unsigned int
> > level,
> > +/*
> > + * Read a file data page for Merkle tree construction. Do
> > aggressive readahead,
> > + * since we're sequentially reading the entire file.
> > + */
> > +static struct page *read_file_data_page(struct inode *inode,
> > + struct file_ra_state *ra,
> > + struct file *filp,
> > + pgoff_t index,
> > + pgoff_t num_pages_in_file)
> > +{
> > + struct page *page;
> > +
> > + page = find_get_page(inode->i_mapping, index);
> > + if (!page || !PageUptodate(page)) {
> > + if (page)
> > + put_page(page);
>
>
> It looks like that there is not necessary check here. If we have NULL
> pointer on page then we will not enter inside. But if we have valid
> pointer on page then we have double check inside. Am I correct?
>
I'm not sure what you mean. This code does the page_cache_sync_readahead() and
read_mapping_page() if either the page is not in the pagecache at all *or* is
not up to date. I know this is slightly different logic than
generic_file_buffered_read() uses, and is suboptimal since the use of
read_mapping_page() causes a redundant pagecache lookup. But we don't need to
squeeze out every possible bit of performance here.
Hmm, maybe it should only call page_cache_sync_readahead() when page == NULL
though. I'll check the readahead code again.
>
> > + page_cache_sync_readahead(inode->i_mapping, ra, filp,
> > + index, num_pages_in_file -
> > index);
> > + page = read_mapping_page(inode->i_mapping, index,
> > NULL);
> > + if (IS_ERR(page))
> > + return page;
>
> Could we recieve the NULL pointer here? Is callee ready to process theNULL return value?
>
No, read_mapping_page() returns either a valid page or an ERR_PTR().
- Eric
prev parent reply other threads:[~2019-12-04 18:18 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-03 19:30 [PATCH] fs-verity: implement readahead for FS_IOC_ENABLE_VERITY Eric Biggers
2019-12-04 7:53 ` Vyacheslav Dubeyko
2019-12-04 18:10 ` Eric Biggers [this message]
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