Re: [PATCH v3] mm: readahead: make thp readahead conditional to mmap_miss logic

[Roman Gushchin]

Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> writes:

> On Mon,  6 Oct 2025 10:51:06 -0700 Roman Gushchin <roman.gushchin@xxxxxxxxx> wrote:
>
>> Commit 4687fdbb805a ("mm/filemap: Support VM_HUGEPAGE for file mappings")
>> introduced a special handling for VM_HUGEPAGE mappings: even if the
>> readahead is disabled, 1 or 2 HPAGE_PMD_ORDER pages are
>> allocated.
>
> Three years ago.
>
>> This change causes a significant regression
>
> So no backport suggested?  I guess reasonable given how long 4687fdbb805a has
> been in tree.

Yes, this was my thinking. Also you need a very specific setup to reveal
this regression.

>> Signed-off-by: Roman Gushchin <roman.gushchin@xxxxxxxxx>
>> Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
>> Cc: Jan Kara <jack@xxxxxxx>
>> Cc: Dev Jain <dev.jain@xxxxxxx>
>
> But I'll slap the Fixes: in there, it might help someone.

I'd do exactly what you suggested: Fixes + no stable backport.

But I guess it still might end up in the LTS tree thanks to
the automation picking up all fixes. Should be ok too.

Thanks!