On 2024/9/26 09:59, Huang, Ying wrote:
Nhat Pham <nphamcs@xxxxxxxxx> writes:
On Tue, Sep 24, 2024 at 6:53 PM Baolin Wang
<baolin.wang@xxxxxxxxxxxxxxxxx> wrote:
One benefit I can mention is that removing 'SWAP_MAP_SHMEM' can help to
batch free shmem swap entries in __swap_entries_free(), similar to the
commit bea67dcc5eea ("mm: attempt to batch free swap entries for
zap_pte_range()") did, which can improve the performance of shmem mTHP
munmap() function based on my testing.
Yeah, the problem with having an extraneous state is you have to
constantly check for it in code, and/or keep it in mind when you
develop things. I've been constantly having to check for this state
when I develop code around this area, and it gets old fast.
If we can use it to optimize something, I can understand keeping it.
But it just seems like dead code to me :)
My preference is to do this as simply as possible - add another case
(usage == 1, nr > 1, and we need to add swap continuations) in the
check in __swap_duplicate()'s first loop, and just WARN right there.
That case CANNOT happen UNLESS we introduce a bug, or have a new use
case. When we actually have a use case, we can always introduce
handling/fallback logic for that case.
Barry, Yosry, Baolin, Ying, how do you feel about this?
Sounds good to me to just WARN now. We can always improve when it's
necessary.
+1. Agreed.
