Re: [PATCH RFC V2 0/6] rxe_map_mr_sg() fix cleanup and refactor

[Zhu Yanjun]

在 2023/11/9 10:24, Zhijian Li (Fujitsu) 写道:
> On 06/11/2023 21:58, Zhu Yanjun wrote:
> > 在 2023/11/6 12:07, Zhijian Li (Fujitsu) 写道:
> > > On 03/11/2023 21:00, Zhu Yanjun wrote:
> > > > 在 2023/11/3 17:55, Li Zhijian 写道:
> > > > > I don't collect the Reviewed-by to the patch1-2 this time, since i
> > > > > think we can make it better.
> > > > >
> > > > > Patch1-2: Fix kernel panic[1] and benifit to make srp work again.
> > > > >              Almost nothing change from V1.
> > > > > Patch3-5: cleanups # newly add
> > > > > Patch6: make RXE support PAGE_SIZE aligned mr # newly add, but not fully tested
> > > > >
> > > > > My bad arm64 mechine offten hangs when doing blktests even though i use the
> > > > > default siw driver.
> > > > >
> > > > > - nvme and ULPs(rtrs, iser) always registers 4K mr still don't supported yet.
> > > > Zhijian
> > > >
> > > > Please read carefully the whole discussion about this problem. You will find a lot of valuable suggestions, especially suggestions from Jason.
> > > Okay, i will read it again. If you can tell me which thread, that would be better.
> > >
> > >
> > > >    From the whole discussion, it seems that the root cause is very clear.
> > > > We need to fix this prolem. Please do not send this kind of commits again.
> > > Let's think about what's our goal first.
> > >
> > > - 1) Fix the panic[1] and only support PAGE_SIZE MR
> > > - 2) support PAGE_SIZE aligned MR
> > > - 3) support any page_size MR.
> > >
> > > I'm sorry i'm not familiar with the linux MM subsystem. It seem it's safe/correct to access
> > > address/memory across pages start from the return of kmap_loca_page(page).
> > > In other words, 2) is already native supported, right?
> > Yes. Please read the comments from Jason, Leon and Bart. They shared a lot of good advice.
> I read the whole discussion again, but I believed i still missed a lost.
>
>
> >  From them, we can know the root cause and how to fix this problem.
> I don't think i misunderstood the root cause:
> RXE splits memory into PAGE_SIZE units in the xarray. As a result, when we extract an address from the xarray,
> we should not access address beyond a PAGE_SIZE window.

This is a complicated problem and it is deeply involved with memory 
management.

A guy who is very familiar with linux MM is to provide a better solution 
to this problem.

I expect a whole perfect solution to this problem.

Zhu Yanjun

> IIUC, then how to fix it?
> - I'm not going to "removing page_size set", it's out of this patch scope.
>     Feel free to do the cleanup separately.
> - I'm not going to fix the NVMe/rtrs etc problems in this patch set when 64K page is enabled.
>     But RXE will tell its callers explicitly "RXE don't don't support such page_size"
> - I didn't state RXE supports PAGE_SIZE aligned page_size MR before refactoring rxe_map_mr_sg(),
>     because I worry about it was not correct to access address beyond the PAGE_SIZE window.
>
> What I should do next?
> Just state "RXE support PAGE_SIZE aligned MR" ? Then patches become
> RDMA/rxe: RDMA/rxe: don't allow registering !PAGE_SIZE aligned MR
> RDMA/rxe: set RXE_PAGE_SIZE_CAP to starting from PAGE_SIZE
>
> Or just keep we have done in the V1
>
> Thanks
>
>
> > Good Luck.
> >
> > Zhu Yanjun
> >
> > > I get totally confused now.
> > >
> > >
> > >
> > > > Zhu Yanjun
> > > >
> > > > > [1] https://lore.kernel.org/all/CAHj4cs9XRqE25jyVw9rj9YugffLn5+f=1znaBEnu1usLOciD+g@xxxxxxxxxxxxxx/T/
> > > > >
> > > > > Li Zhijian (6):
> > > > >      RDMA/rxe: RDMA/rxe: don't allow registering !PAGE_SIZE mr
> > > > >      RDMA/rxe: set RXE_PAGE_SIZE_CAP to PAGE_SIZE
> > > > >      RDMA/rxe: remove unused rxe_mr.page_shift
> > > > >      RDMA/rxe: Use PAGE_SIZE and PAGE_SHIFT to extract address from
> > > > >        page_list
> > > > >      RDMA/rxe: cleanup rxe_mr.{page_size,page_shift}
> > > > >      RDMA/rxe: Support PAGE_SIZE aligned MR
> > > > >
> > > > >     drivers/infiniband/sw/rxe/rxe_mr.c    | 80 ++++++++++++++++-----------
> > > > >     drivers/infiniband/sw/rxe/rxe_param.h |  2 +-
> > > > >     drivers/infiniband/sw/rxe/rxe_verbs.h |  9 ---
> > > > >     3 files changed, 48 insertions(+), 43 deletions(-)