在 2020/4/21 上午6:11, Johannes Weiner 写道: > The try/commit/cancel protocol that memcg uses dates back to when > pages used to be uncharged upon removal from the page cache, and thus > couldn't be committed before the insertion had succeeded. Nowadays, > pages are uncharged when they are physically freed; it doesn't matter > whether the insertion was successful or not. For the page cache, the > transaction dance has become unnecessary. > > Introduce a mem_cgroup_charge() function that simply charges a newly > allocated page to a cgroup and sets up page->mem_cgroup in one single > step. If the insertion fails, the caller doesn't have to do anything > but free/put the page. > > Then switch the page cache over to this new API. > > Subsequent patches will also convert anon pages, but it needs a bit > more prep work. Right now, memcg depends on page->mapping being > already set up at the time of charging, so that it can maintain its > own MEMCG_CACHE and MEMCG_RSS counters. For anon, page->mapping is set > under the same pte lock under which the page is publishd, so a single > charge point that can block doesn't work there just yet. > > The following prep patches will replace the private memcg counters > with the generic vmstat counters, thus removing the page->mapping > dependency, then complete the transition to the new single-point > charge API and delete the old transactional scheme. > > Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx> > --- Reviewed-by: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx>
