* Vlastimil Babka: > preadv2(RWF_NOWAIT) can be used to open a side-channel to pagecache > contents, as it reveals metadata about residency of pages in > pagecache. > > If preadv2(RWF_NOWAIT) returns immediately, it provides a clear "page > not resident" information, and vice versa. > > Close that sidechannel by always initiating readahead on the cache if > we encounter a cache miss for preadv2(RWF_NOWAIT); with that in place, > probing the pagecache residency itself will actually populate the > cache, making the sidechannel useless. I think this needs to use a different flag because the semantics are so much different. If I understand this change correctly, previously, RWF_NOWAIT essentially avoided any I/O, and now it does not. Thanks, Florian
