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Date:   Wed, 7 Apr 2021 16:02:55 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Daeho Jeong <daehojeong@google.com>
Cc:     Chao Yu <yuchao0@huawei.com>, Jaegeuk Kim <jaegeuk@kernel.org>,
        linux-fsdevel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net
Subject: Why use page_cache_ra_unbounded?
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commit 5fdb322ff2c2b4ad519f490dcb7ebb96c5439af7
Author: Daeho Jeong <daehojeong@google.com>
Date:   Thu Dec 3 15:56:15 2020 +0900

    f2fs: add F2FS_IOC_DECOMPRESS_FILE and F2FS_IOC_COMPRESS_FILE

+       page_cache_ra_unbounded(&ractl, len, 0);

/**
 * page_cache_ra_unbounded - Start unchecked readahead.
 * @ractl: Readahead control.
 * @nr_to_read: The number of pages to read.
 * @lookahead_size: Where to start the next readahead.
 *
 * This function is for filesystems to call when they want to start
 * readahead beyond a file's stated i_size.  This is almost certainly
 * not the function you want to call.  Use page_cache_async_readahead()
 * or page_cache_sync_readahead() instead.
 *
 * Context: File is referenced by caller.  Mutexes may be held by caller.
 * May sleep, but will not reenter filesystem to reclaim memory.
 */

Why?