On Fri, Nov 29, 2024 at 3:25 PM chenridong <chenridong@xxxxxxxxxx> wrote: > > > > On 2024/11/29 7:08, Barry Song wrote: > > On Mon, Nov 25, 2024 at 2:19 PM chenridong <chenridong@xxxxxxxxxx> wrote: > >> > >> > >> > >> On 2024/11/18 12:21, Matthew Wilcox wrote: > >>> On Mon, Nov 18, 2024 at 05:14:14PM +1300, Barry Song wrote: > >>>> On Mon, Nov 18, 2024 at 5:03 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > >>>>> > >>>>> On Sat, Nov 16, 2024 at 09:16:58AM +0000, Chen Ridong wrote: > >>>>>> 2. In shrink_page_list function, if folioN is THP(2M), it may be splited > >>>>>> and added to swap cache folio by folio. After adding to swap cache, > >>>>>> it will submit io to writeback folio to swap, which is asynchronous. > >>>>>> When shrink_page_list is finished, the isolated folios list will be > >>>>>> moved back to the head of inactive lru. The inactive lru may just look > >>>>>> like this, with 512 filioes have been move to the head of inactive lru. > >>>>> > >>>>> I was hoping that we'd be able to stop splitting the folio when adding > >>>>> to the swap cache. Ideally. we'd add the whole 2MB and write it back > >>>>> as a single unit. > >>>> > >>>> This is already the case: adding to the swapcache doesn’t require splitting > >>>> THPs, but failing to allocate 2MB of contiguous swap slots will. > >>> > >>> Agreed we need to understand why this is happening. As I've said a few > >>> times now, we need to stop requiring contiguity. Real filesystems don't > >>> need the contiguity (they become less efficient, but they can scatter a > >>> single 2MB folio to multiple places). > >>> > >>> Maybe Chris has a solution to this in the works? > >>> > >> > >> Hi, Chris, do you have a better idea to solve this issue? > > > > Not Chris. As I read the code again, we have already the below code to fixup > > the issue "missed folio_rotate_reclaimable()" in evict_folios(): > > > > /* retry folios that may have missed > > folio_rotate_reclaimable() */ > > list_move(&folio->lru, &clean); > > > > It doesn't work for you? > > > > commit 359a5e1416caaf9ce28396a65ed3e386cc5de663 > > Author: Yu Zhao <yuzhao@xxxxxxxxxx> > > Date: Tue Nov 15 18:38:07 2022 -0700 > > mm: multi-gen LRU: retry folios written back while isolated > > > > The page reclaim isolates a batch of folios from the tail of one of the > > LRU lists and works on those folios one by one. For a suitable > > swap-backed folio, if the swap device is async, it queues that folio for > > writeback. After the page reclaim finishes an entire batch, it puts back > > the folios it queued for writeback to the head of the original LRU list. > > > > In the meantime, the page writeback flushes the queued folios also by > > batches. Its batching logic is independent from that of the page reclaim. > > For each of the folios it writes back, the page writeback calls > > folio_rotate_reclaimable() which tries to rotate a folio to the tail. > > > > > > folio_rotate_reclaimable() only works for a folio after the page reclaim > > has put it back. If an async swap device is fast enough, the page > > writeback can finish with that folio while the page reclaim is still > > working on the rest of the batch containing it. In this case, that folio > > will remain at the head and the page reclaim will not retry it before > > reaching there. > > > > This patch adds a retry to evict_folios(). After evict_folios() has > > finished an entire batch and before it puts back folios it cannot free > > immediately, it retries those that may have missed the rotation. > > Before this patch, ~60% of folios swapped to an Intel Optane missed > > folio_rotate_reclaimable(). After this patch, ~99% of missed folios were > > reclaimed upon retry. > > > > This problem affects relatively slow async swap devices like Samsung 980 > > Pro much less and does not affect sync swap devices like zram or zswap at > > all. > > > >> > >> Best regards, > >> Ridong > > > > Thanks > > Barry > > Thank you for your reply, Barry. > I found this issue with 5.10 version. I reproduced this issue with the > next version, but the CONFIG_LRU_GEN_ENABLED kconfig is disabled. I > tested again with CONFIG_LRU_GEN_ENABLED enabled, and this issue can be > fixed. > > IIUC, the 359a5e1416caaf9ce28396a65ed3e386cc5de663 commit can only work > when CONFIG_LRU_GEN_ENABLED is enabled, but this issue exists when > CONFIG_LRU_GEN_ENABLED is disabled and it should be fixed. > > I read the code of commit 359a5e1416caaf9ce28396a65ed3e386cc5de663, it > found folios that are missed to rotate in a more complicated way, but it > makes it much clearer what is being done. Should I implement in Yu > Zhao's way? yes. this is completely the same thing. since Yu only fixed in mglru and you are still using active/inactive, the same fix should apply to active/inactive lru. > > Best regards, > Ridong thanks barry
