On Wed, 5 Feb 2014 11:16:49 +0400 Vladimir Davydov <vdavydov@xxxxxxxxxxxxx> wrote: > > So why did I originally make DEFAULT_SEEKS=2? Because I figured that to > > recreate (say) an inode would require a seek to the inode data then a > > seek back. Is it legitimate to include the > > seek-back-to-what-you-were-doing-before seek in the cost of an inode > > reclaim? I guess so... > > Hmm, that explains this 2. Since we typically don't need to "seek back" > when recreating a cache page, as they are usually read in bunches by > readahead, the number of seeks to bring back a user page is 1, while the > number of seeks to recreate an average inode is 2, right? Sounds right to me. > Then to scan inodes and user pages so that they would generate > approximately the same number of seeks, we should calculate the number > of objects to scan as follows: > > nr_objects_to_scan = nr_pages_scanned / lru_pages * > nr_freeable_objects / > shrinker->seeks > > where shrinker->seeks = DEFAULT_SEEKS = 2 for inodes. hm, I wonder if we should take the size of the object into account. Should we be maximizing (memory-reclaimed / seeks-to-reestablish-it). > But currently we > have four times that. I can explain why we should multiply this by 2 - > we do not count pages moving from active to inactive lrus in > nr_pages_scanned, and 2*nr_pages_scanned can be a good approximation for > that - but I have no idea why we multiply it by 4... I don't understand this code at all: total_scan = nr; delta = (4 * nr_pages_scanned) / shrinker->seeks; delta *= freeable; do_div(delta, lru_pages + 1); total_scan += delta; If it actually makes any sense, it sorely sorely needs documentation. David, you touched it last. Any hints? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>