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

["yukuai (C)" <yukuai3@huawei.com>]

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