> > > So there are two separate problems mentioned here. The first is to > > ensure that readahead (RA) pages are treated as more disposable than > > accessed pages under memory pressure and then to derive a statistic for > > futile RA (those pages that were read in but never accessed). > > > > The first sounds really like its an LRU thing rather than adding yet > > another page flag. We need a position in the LRU list for never > > accessed ... that way they're first to be evicted as memory pressure > > rises. > > > > The second is you can derive this futile readahead statistic from the > > LRU position of unaccessed pages ... you could keep this globally. > > > > Now the problem: if you trash all unaccessed RA pages first, you end up > > with the situation of say playing a movie under moderate memory > > pressure that we do RA, then trash the RA page then have to re-read to display > > to the user resulting in an undesirable uptick in read I/O. > > James - now that I'm thinking about it. I think the movie should be fine because when we calculate the read-hit from RA'd pages, the movie RA blocks will get a good hit-ratio and hence it's RA'd blocks won't be touched. But then we might need to track the hit-ratio at the RA-block(?) level. Chetan -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
