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AJvYcCUI+ryHFr1PrMdh1FY8GZtq1O4awCv29qCkqPEOgPqu4lwFIm4q6+34nwElmbMcQdk2EkQOk1SaWbAYUZJHsSTf2RE= X-Gm-Message-State: AOJu0YyiWsBx52TThMCGNf/OLqOBID+XWRwBr1QGtBf0okScdNOvp+vm qVU9LsmzqKfQUaUbLj+aHZwgQ4/q0Gz6Tz9kFmt5WIoPi2Q7slCg+R5JtU9JjEgvkUGlR414Ty9 e5aITbE+uYPNmImSEltNAJHr2ONBYJOFKCalC X-Google-Smtp-Source: AGHT+IGBuCU23m+wrmkFzQkUCc4DL4NBFPm8xZ6GTjzrHf41bNowvPfktB6PfvqelK6j4q2T/3ufnLal/dwQaerFDnk= X-Received: by 2002:a17:907:cbc9:b0:a6f:b193:758e with SMTP id a640c23a62f3a-a70385e67dfmr488672466b.29.1719257680243; Mon, 24 Jun 2024 12:34:40 -0700 (PDT) MIME-Version: 1.0 References: <202406241651.963e3e78-oliver.sang@intel.com> In-Reply-To: From: Yosry Ahmed Date: Mon, 24 Jun 2024 12:34:04 -0700 Message-ID: Subject: Re: [linux-next:master] [mm] 0fa2857d23: WARNING:at_mm/page_alloc.c:#__alloc_pages_noprof To: Matthew Wilcox Cc: kernel test robot , Usama Arif , oe-lkp@lists.linux.dev, lkp@intel.com, Linux Memory Management List , Andrew Morton , Chengming Zhou , Nhat Pham , David Hildenbrand , "Huang, Ying" , Hugh Dickins , Johannes Weiner , Shakeel Butt , Andi Kleen , linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 7B2501C000B X-Stat-Signature: m843gisftqqjm5fraib91n8rtix683we X-Rspam-User: X-HE-Tag: 1719257682-979130 X-HE-Meta: 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 DAZi5+Y0 GocHWqI5Zm672QY6N/u4CM7ZfU6xJ52cBFAevRnvZNhSkgHnUTB/rXdKwbSCCmDyayIGMAvedErNxt/padaB12hIhEeZI68vAA/ciHx39NeDJuF7zK3+aLpbBlfQaN6dTNO2l06LC/or1jiX2SMdCpBmpg0NVimjxJn90GMowAJeiHOgTz9T2lhEzODMyCj9eFQaZ5pQus3HKPxarYHQFeyFyGuyCIPPGAsazT2t76OISVPrx+4aBbN4Ic6MAQY9LIENlZzUV19Et5HNqiBv+BqynKw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000023, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Jun 24, 2024 at 12:26=E2=80=AFPM Matthew Wilcox wrote: > > On Mon, Jun 24, 2024 at 11:57:45AM -0700, Yosry Ahmed wrote: > > On Mon, Jun 24, 2024 at 11:56=E2=80=AFAM Matthew Wilcox wrote: > > > > > > On Mon, Jun 24, 2024 at 11:53:30AM -0700, Yosry Ahmed wrote: > > > > After a page is swapped out during reclaim, __remove_mapping() will > > > > call __delete_from_swap_cache() to replace the swap cache entry wit= h a > > > > shadow entry (which is an xa_value). > > > > > > Special entries are disjoint from shadow entries. Shadow entries hav= e > > > the last two bits as 01 or 11 (are congruent to 1 or 3 modulo 4). > > > Special entries have values below 4096 which end in 10 (are congruent > > > to 2 modulo 4). > > > > You are implying that we would no longer have a shadow entry for such > > zero folios, because we will be storing a special entry instead. > > Right? > > umm ... maybe I have a misunderstanding here. > > I'm saying that there wouldn't be a _swap_ entry here because the folio > wouldn't be stored anywhere on the swap device. But there could be a > _shadow_ entry. Although if the page is full of zeroes, it was probably > never referenced and doesn't really need a shadow entry. Is it possible to have a shadow entry AND a special entry (e.g. XA_ZERO_ENTRY) at the same index? This is what would be required to maintain the current behavior (assuming we really need the shadow entries for such zeroed folios).