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[173.79.60.52]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-9123bed0aaesm2890416d6.41.2026.09.15.10.00.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 15 Sep 2026 10:00:33 -0700 (PDT) Date: Tue, 15 Sep 2026 13:00:31 -0400 From: Gregory Price To: "Lorenzo Stoakes (ARM)" Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, akpm@linux-foundation.org, liam@infradead.org, david@kernel.org, vbabka@kernel.org, jannh@google.com, wangjiexun@tinylab.org, sashiko-bot , stable@vger.kernel.org Subject: Re: [PATCH] mm/madvise: reclaim isolated folios if PTE restart fails Message-ID: References: <20260912110832.3203902-1-gourry@gourry.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 0BCCAC0009 X-Stat-Signature: 8ehrwrsgd6q9wxxtr63suhp8d8hyb1j8 X-HE-Tag: 1789491634-994261 X-HE-Meta: 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 G0Cxprll fn8ph8I+XZxsN2zSmj97+9eQXpnR3Et32Zc9KrhTRdvn4MXEO1xklxwzsxTbZI/I68ulbaoPJYMdGY2IbGWbAtRH9ZEGZJEhbxkyCaPQaNkDpwLg8KmHjNI9490YzTg5JSuXghWaq2uDdi4nmwkNF6+lkPzx0yKbQL5QX+A0eZgW8JVHkiAOKT/VenZ9cJgHgSmenS96ryIcpbDsls86ldNmtfLYccOgY9YqmoyL6HhOaOa9e8BMQrIQHo4wPwgIje/CcxnjzZU4tkzmyK7kxcapGJqjC178AEY6oiqjJhzSlLI4n8EnHEcNsLkoVjnhIqVoRedWpHTx8Www524A/pBgLTwtYwisqopgTMCsiQvhfnV0wwXVPv+OpZ/xELiOJtcf2hrBZE/zp9RhdulmAkS7r30Oh//E++sNk9iy4FAMTDaoOQh0zudYpC7+a+wALCH0R/QcavXRXOg0= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Sep 15, 2026 at 04:55:47PM +0100, Lorenzo Stoakes (ARM) wrote: > > diff --git a/mm/madvise.c b/mm/madvise.c > > index 574aa2bb7c7e..ba5a3d77241a 100644 > > --- a/mm/madvise.c > > +++ b/mm/madvise.c > > @@ -464,7 +464,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd, > > This function is truly some of the absolute worst code I've read in > mm. Shocking. > relevant meme: https://i.imgur.com/W0N40BK.png No argument here. This function in particular is really horrendous. I think i'm now 4 or 5 stacks deep on the "Thanks for fixing a bug, but while reviewing your fix sashiko found yet another CVE-worthy bug". I'm convinced (like you below) madvise needs some attention. > > restart: > > start_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl); > > if (!start_pte) > > - return 0; > > + goto out; > > flush_tlb_batched_pending(mm); > > lazy_mmu_mode_enable(); > > for (; addr < end; pte += nr, addr += nr * PAGE_SIZE) { > > @@ -568,6 +568,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd, > > folio_deactivate(folio); > > } > > > > +out: > > Seems odd to put this here for a condition that explicitly guarantees > !start_pte? It should be before the if (pageout) reclaim_pages(...); > surely? > I wanted to prevent any future use of the label from skipping the start_pte check. The function is so bad I was err'ing on the side of being a bit defensive without making it worse. I suppose reasonable to say the goto is worse. > I honestly wonder whether, rather than adding yet another label/goto into this > absolute bloody mess, whether we should just live with a bit of duplication and do: > > if (!start_pte) { > if (pageout) > reclaim_pages(&folio_list); > return 0; > } > > I actually think that'd be clearer at this point than throwing in some more > indirection. > I'll spin a v2. > That's for the backport but somebody needs to rework this entire bloody > function going forwards... The longer I look at madvise, the more I think it is a wart on mm/ as-written. A userland-driven page table walker that requires all the special-casing of Yooj Pages, zone device, swap, soft leafs, a bunch of tlb flushing 5-tabs deep... Scary surface. I've been trying to think about how we might make this more reasonable, but generalizing the different walkers across mm is pretty hard. ~Gregory