On Thu, Sep 5, 2024 at 9:30 AM Usama Arif <usamaarif642@xxxxxxxxx> wrote: > > > > On 03/09/2024 23:05, Yosry Ahmed wrote: > > On Tue, Sep 3, 2024 at 2:36 PM Barry Song <21cnbao@xxxxxxxxx> wrote: > >> > >> On Wed, Sep 4, 2024 at 8:08 AM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > >>> > >>> On Tue, 3 Sep 2024 11:38:37 -0700 Yosry Ahmed <yosryahmed@xxxxxxxxxx> wrote: > >>> > >>>>> [ 39.157954] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000007 > >>>>> [ 39.158288] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001 > >>>>> [ 39.158634] R13: 0000000000002b9a R14: 0000000000000000 R15: 00007ffd619d5518 > >>>>> [ 39.158998] </TASK> > >>>>> [ 39.159226] ---[ end trace 0000000000000000 ]--- > >>>>> > >>>>> After reverting this or Usama's "mm: store zero pages to be swapped > >>>>> out in a bitmap", the problem is gone. I think these two patches may > >>>>> have some conflict that needs to be resolved. > >>>> > >>>> Yup. I saw this conflict coming and specifically asked for this > >>>> warning to be added in Usama's patch to catch it [1]. It served its > >>>> purpose. > >>>> > >>>> Usama's patch does not handle large folio swapin, because at the time > >>>> it was written we didn't have it. We expected Usama's series to land > >>>> sooner than this one, so the warning was to make sure that this series > >>>> handles large folio swapin in the zeromap code. Now that they are both > >>>> in mm-unstable, we are gonna have to figure this out. > >>>> > >>>> I suspect Usama's patches are closer to land so it's better to handle > >>>> this in this series, but I will leave it up to Usama and > >>>> Chuanhua/Barry to figure this out :) > >> > >> I believe handling this in swap-in might violate layer separation. > >> `swap_read_folio()` should be a reliable API to call, regardless of > >> whether `zeromap` is present. Therefore, the fix should likely be > >> within `zeromap` but not this `swap-in`. I’ll take a look at this with > >> Usama :-) > > > > I meant handling it within this series to avoid blocking Usama > > patches, not within this code. Thanks for taking a look, I am sure you > > and Usama will figure out the best way forward :) > > Hi Barry and Yosry, > > Is the best (and quickest) way forward to have a v8 of this with > https://lore.kernel.org/all/20240904055522.2376-1-21cnbao@xxxxxxxxx/ > as the first patch, and using swap_zeromap_entries_count in alloc_swap_folio > in this support large folios swap-in patch? Yes, Usama. i can actually do a check: zeromap_cnt = swap_zeromap_entries_count(entry, nr); /* swap_read_folio() can handle inconsistent zeromap in multiple entries */ if (zeromap_cnt > 0 && zeromap_cnt < nr) try next order; On the other hand, if you read the code of zRAM, you will find zRAM has exactly the same mechanism as zeromap but zRAM can even do more by same_pages filled. since zRAM does the job in swapfile layer, there is no this kind of consistency issue like zeromap. So I feel for zRAM case, we don't need zeromap at all as there are duplicated efforts while I really appreciate your job which can benefit all swapfiles. i mean, zRAM has the ability to check "zero"(and also non-zero but same content). after zeromap checks zeromap, zRAM will check again: static int zram_write_page(struct zram *zram, struct page *page, u32 index) { ... if (page_same_filled(mem, &element)) { kunmap_local(mem); /* Free memory associated with this sector now. */ flags = ZRAM_SAME; atomic64_inc(&zram->stats.same_pages); goto out; } ... } So it seems that zeromap might slightly impact my zRAM use case. I'm not blaming you, just pointing out that there might be some overlap in effort here :-) > > Thanks, > Usama Thanks Barry
