在 2019/8/24 上午9:59, Hugh Dickins 写道: > On Wed, 21 Aug 2019, Alex Shi wrote: >> 在 2019/8/21 上午2:24, Hugh Dickins 写道: >>> I'll set aside what I'm doing, and switch to rebasing ours to v5.3-rc >>> and/or mmotm. Then compare with what Alex has, to see if there's any >>> good reason to prefer one to the other: if no good reason to prefer ours, >>> I doubt we shall bother to repost, but just use it as basis for helping >>> to review or improve Alex's. >> >> For your review, my patchset are pretty straight and simple. >> It just use per lruvec lru_lock to replace necessary pgdat lru_lock. >> just this. We could talk more after I back to work. :) > > Sorry to be bearer of bad news, Alex, but when you said "straight and > simple", I feared that your patchset would turn out to be fundamentally > too simple. > > And that is so. I have only to see the > lruvec = mem_cgroup_page_lruvec(page, pgdat); > line in isolate_migratepages_block() in mm/compaction.c, and check > that mem_cgroup_page_lruvec() is little changed in mm/mempolicy.c. > > The central problem with per-memcg lru_lock is that you do not know > for sure what lock to take (which memcg a page belongs to) until you > have taken the expected lock, and then checked whether page->memcg > is still the same - backing out and trying again if not. > > Fix that central problem, and you end up with a more complicated > patchset, much like ours. It's true that when ours was first developed, > the memcg situation was more complicated in several ways, and perhaps > some aspects of our patchset could be simplified now (though I've not > identified any). Johannes in particular has done a great deal of > simplifying work in memcg over the last few years, but there are still > situations in which a page's memcg can change (move_charge_at_immigrate > and swapin readahead spring to mind - or perhaps the latter is only an > issue when MEMCG_SWAP is not enabled, I forget; and I often wonder if > reparenting will be brought back one day). > > I did not review your patchset in detail, and wasn't able to get very > far in testing it. At first I was put off by set_task_reclaim_state > warnings from mm/vmscan.c, but those turned out to be in v5.3-rc5 > itself, not from your patchset or mine (but I've not yet investigated > what's responsible for them). Within a minute of starting swapping > load, kcompactd compact_lock_irqsave() in isolate_migratepages_block() > would deadlock, and I did not get further. (Though I did also notice > that booting the CONFIG_MEMCG=y kernel with "cgroup_disable=memory" > froze in booting - tiresomely, one has to keep both the memcg and > no-memcg locking to cope with that case, and I guess you had not.) > > Rather than duplicating effort, I would advise you to give our patchset > a try, and if it works for you, help towards getting that one merged: > but of course, it's up to you. Thanks a lot for all infos and reminders! Yes, the page->memcg change would be a problem. I will studying your patchset and try to merge them. > > I've attached a tarfile of it rebased to v5.3-rc5: I do not want to > spam the list with patches yet, because I do not have any stats or > argument in support of the series, as Andrew asked for years ago and > Michal asks again now. But aside from that I consider it ready, and > will let Shakeel take it over from here, while I get back to what I > diverted from (but of course I'll try to answer questions on it). > I will trying to look into them. Thanks for your kindly offer. :) Thanks! Alex
