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References: <YXHK5HrQpJu9oy8w@casper.infradead.org>
 <87tuh9n9w2.fsf@vps.thesusis.net> <20211022084127.GA1026@quack2.suse.cz>
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From:   Phillip Susi <phill@thesusis.net>
To:     Jan Kara <jack@suse.cz>
Cc:     Matthew Wilcox <willy@infradead.org>,
        linux-fsdevel@vger.kernel.org,
        Phillip Lougher <phillip@squashfs.org.uk>,
        linux-erofs@lists.ozlabs.org, linux-btrfs@vger.kernel.org,
        linux-ntfs-dev@lists.sourceforge.net, ntfs3@lists.linux.dev,
        linux-bcache@vger.kernel.org, David Howells <dhowells@redhat.com>,
        Hsin-Yi Wang <hsinyi@chromium.org>
Subject: Re: Readahead for compressed data
Date:   Mon, 25 Oct 2021 14:59:45 -0400
In-reply-to: <20211022084127.GA1026@quack2.suse.cz>
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Jan Kara <jack@suse.cz> writes:

> Well, one of the problems with keeping compressed data is that for mmap(2)
> you have to have pages decompressed so that CPU can access them. So keeping
> compressed data in the page cache would add a bunch of complexity. That
> being said keeping compressed data cached somewhere else than in the page
> cache may certainly me worth it and then just filling page cache on demand
> from this data...

True... Did that multi generational LRU cache ever get merged?  I was
thinking you could use that to make sure that the kernel prefers to
reclaim the decompressed pages in favor of keeping the compressed ones
around.