linux-kernel - Re: [PATCH] mm: memory: Force-inline PTE/PMD zapping functions for performance

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Message-ID: <2a1b7ebc-f27c-444e-be89-df14ac1dc97d@lucifer.local>
Date: Mon, 4 Aug 2025 14:59:02 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Li Qiang <liqiang01@...inos.cn>
Cc: akpm@...ux-foundation.org, david@...hat.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Liam.Howlett@...cle.com, vbabka@...e.cz,
        rppt@...nel.org, surenb@...gle.com, mhocko@...e.com
Subject: Re: [PATCH] mm: memory: Force-inline PTE/PMD zapping functions for
 performance

OK,

So I hacked -fopt-info-inline-all into the mm/ Makefile in a rather quick and
dirty way and it seems some stuff gets inlined locally, but we're mostly hitting
the '--param max-inline-insns-single limit reached' limit here.

Which maybe is just a point where the compiler possibly arbitrarily gives up?

Vlasta rightly pointed out off-list that given this appears to only be used in
one place you'd expect inlining as register spill isn't such a concern (we'll
spill saving the stack before function invocation anyway).

So there might actually be some validity here?

This is gcc 15.1.1 running on an x86-64 platform by the way.

mm/memory.c:1871:10: optimized:  Inlined zap_p4d_range/6380 into unmap_page_range/6381 which now has time 1458.996712 and size 65, net change of -11.
mm/memory.c:1850:10: optimized:  Inlined zap_pud_range.isra/8017 into zap_p4d_range/6380 which now has time 10725.428482 and size 29, net change of -12.
mm/memory.c:1829:10: missed:   not inlinable: zap_pud_range.isra/8017 -> zap_pmd_range.isra/8018, --param max-inline-insns-single limit reached
mm/memory.c:1800:10: missed:   not inlinable: zap_pmd_range.isra/8018 -> zap_pte_range/6377, --param max-inline-insns-auto limit reached
mm/memory.c:1708:8: optimized:  Inlined do_zap_pte_range.constprop/7983 into zap_pte_range/6377 which now has time 4244.320854 and size 148, net change of -15.
mm/memory.c:1664:9: missed:   not inlinable: do_zap_pte_range.constprop/7983 -> zap_present_ptes.constprop/7985, --param max-inline-insns-single limit reached

Cheers, Lorenzo