linux-kernel - Re: [RFC] iomap: fix race between readahead and direct write

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Message-ID: <857fa4e7-c529-40cf-9916-151d91e815c4@huawei.com>
Date:   Sun, 19 Jan 2020 09:57:03 +0800
From:   "yukuai (C)" <yukuai3@...wei.com>
To:     Matthew Wilcox <willy@...radead.org>
CC:     <hch@...radead.org>, <darrick.wong@...cle.com>,
        <linux-xfs@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <houtao1@...wei.com>,
        <zhengbin13@...wei.com>, <yi.zhang@...wei.com>
Subject: Re: [RFC] iomap: fix race between readahead and direct write



On 2020/1/19 9:42, Matthew Wilcox wrote:
> Did you read my patch series?  The current code allocates pages,
> but does not put them in the page cache until after iomap is called.
> My patch series changes that to put the pages in the page cache as soon
> as they're allocated, and before iomap is called.

The current code to determin if page need to be allocated:

     page = xa_load(&mapping->i_pages, page_offset);
     if (page && !xa_is_value(page)) {
       /*
       ┊* Page already present?  Kick off the current batch of
       ┊* contiguous pages before continuing with the next
       ┊* batch.
       ┊*/
       if (nr_pages)
         read_pages(mapping, filp, &page_pool, nr_pages,
             gfp_mask);
       nr_pages = 0;
       continue;
     }

     page = __page_cache_alloc(gfp_mask);
     if (!page)
       break;

Page will be allocated if the page do not exist in page cache. And I
don't see your patch series change that. Or am I missing something?

Thanks！
Yu Kuai