Re: [PATCH mm-new] mm/mglru: clarify the generation placement in lru_gen_folio_seq()

[Ridong Chen <ridong.chen@linux.dev>]

On 10/20/2026 1:43 PM, Barry Song wrote:
> On Tue, Oct 20, 2026 at 10:36 AM Ridong Chen <ridong.chen@linux.dev> wrote:
>>
>> From: Ridong Chen <chenridong@xiaomi.com>
>>
>> lru_gen_folio_seq() computes how many generations below max_seq a
>> folio should be added to, but stores it in a variable named "gen".
>> Elsewhere in MGLRU "gen" means an index into lrugen->folios[], i.e.
>> seq % MAX_NR_GENS, so reusing the name for a relative offset is
>> confusing.
>>
>> The comment table above the code also no longer matches it. It only
>> covers the PG_active and the final branch, leaving out the reclaiming
>> and "can't evict yet" cases, and it lists LRU_REFS_FLAGS as an input
>> although lru_gen_folio_seq() never looks at it.
>>
>> Rename the local variable to "age", redraw the table so that each
>> branch maps to the age and seq it produces, and note that the result
>> is clamped to min_seq[type].
>>
>> No functional change.
>>
>> Assisted-by: LLM
>> Signed-off-by: Ridong Chen <chenridong@xiaomi.com>
>> ---
> 
> Hi Ridong,
> 
> The cleanup might be right, but this part is changing rapidly
> with Kairui's MGLRU-FG series. Maybe we should wait until
> that series lands and then see if this cleanup is still needed?
> 
Sure, I'm fine to wait. Looking at MGLRU-FG v4, though, only [4/17]
touches this function, and it mostly adapts the workingset checks to
LRU refs. The local is still called "gen" and the table still leaves
out the reclaiming and "can't evict yet" branches, so the function
stays just as confusing after the series.

Or，Kairui, do you think this is worth cleaning up? If so, would you
mind adding a patch to MGLRU-FG to clean it up, so it doesn't
conflict with your changes?
-- 
Best regards
Ridong