linux-kernel - Regression caused by commit 4687fdbb805a ("mm/filemap: Support VM

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Message-ID: <87plcw8lyq.fsf@linux.dev>
Date: Fri, 15 Aug 2025 11:43:25 -0700
From: Roman Gushchin <roman.gushchin@...ux.dev>
To: Matthew Wilcox <willy@...radead.org>, Andrew Morton
 <akpm@...ux-foundation.org>
Cc: "linux-mm@...ck.org" <linux-mm@...ck.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Regression caused by commit 4687fdbb805a ("mm/filemap: Support
 VM_HUGEPAGE for file mappings")

Hello!

The commit 4687fdbb805a ("mm/filemap: Support VM_HUGEPAGE for file
mappings") causes a regression in our production for containers
which are running short on memory. In some cases they are getting
stuck for hours in a vicious reclaim cycle. Reverting this commit
fixes the problem.

As I understand, the intention of the commit is to allocate large folios
whenever possible, and the idea is to ignore device-specific readahead
settings and the mmap_miss logic to achieve that, which makes total
sense.

However under a heavy memory pressure there must be a mechanism to
revert to order-0 folios, otherwise the memory pressure is inevitable
increased. Maybe mmap_miss heuristics should still be applied? Any other
ideas how to fix it?

Also, a side question: I wonder if it makes sense to allocate 1-2
PMD-sized folios if mapping_large_folio_support() is not there?

Thanks!