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U2FsdGVkX1+Co53gq8sUsxMO34TTVy2wNIrNtCHILQyzcfh7nbubP7JSpv6+QHvLXlmtxK+bWtYUC5Bt6qfZlXRCe8aliYtJ6K53w57D0MLt8vCidNafihWaVFbNGyvWqv/ZvTnjxaVoaEs9JakQ5pFfQxsw/016PTIWZlvXFb7RXHLvGAT/Om2ZSgPFKXkOSlN1Ewtser+D40AHcznTQ2dV8DX16GbjEYl7UORT07TZy+cjLUwkrWjrxF1ec1jLjHIPhfF/hRlFScisHKytmD5Nj6L48iV6oMbMACWHNJRlzPbfTEoPWUORWwR7Aah9s28wDR5wALCMtRVDOc20cxuasa7chElj5faqWL9eDtwCqlF1SW8WB6pRhhgymTIL3Wwiy5O1Mj0m/oTFy6NziDYNIo7A8R6zvUNNKnKsmG/dTnEtlirzScjq+RtM25YYWUnGBTGTTTPE2OxEwAcpMiKTvlDhT0tUkzeXYVpbFv8Ng0fasBwkOyZAdVNiJE57f3efoEx12S9JNIhRexu+OexkfxcVWJ2rH23DWv/znDsLB9Iy+7rSA9yvQhChWVA1cvre6Ij/ZIB8eKnHSD7Xu7bBABDlJnp52UyTWRUg3yJdkLQvL2WGzLAjP5DW3Ko4Lvvh4U/Py+FWxnA38SOxVL0dGrf8u9Pyt9v42HsFtdED7I9zfniaE3Dqisa7HiVcIsLVAuBRf/hI5er1bt5pkphJerb8HGOEgFu8fezpQObuTithJ5NoH1yxdJeeMPQ82ESUmx5vKa+6UKToD9CaBXMyU+6HPts7d6+MqVFkH0bSqALg069CuuuxUQRbAm5S/NeovtWNqXVWsj/kAz4Jp7t7LmAk0at6KJXf+T0beWd7B+c1gAjD75HktMmeaQWPcqBiybJ15qj7sT2jRLmmLlzRBxVLB55K8UCqknanYkesQqiigMsy8OyvLqVvEMqL7DoXUn5vwbPDE6MDFnw jzEb5R6/ WdKtst0rJ/tWApkccD3jOAT9rYn2rAJURNlZbWMeF0afQcX6n6w8dnXjS2Oxxzgks9VN5xH9ork7pAEF6mkhESct8QJhb9BjJ8B5vD0xw9Rdy6fssxYFbwEUu8zDELIy0Asuy2Y4iweFP7N6u08XnP9j2mfIBxV5hJA7XcMqYwUFJhrT79IWAfYjek5f1C6yKNTQa/90xxdyEWG2pnSuGS+ByYE6HzM5iDhHsK3Qn6ZhOLBRQDLmh7Bfw98DbhrLIko9YyrR368y82mm21oE5w5gYV6Y6QT3GsEK4baz4Dz9Es28V9IIcLv2wRxYFvP02wyDTV4PbHdVfw8M7aFKekN2JzVTPnNbWTZbGinCU1Ia/5vq3wbYgWTKdIA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 13 Apr 2026, at 16:20, Matthew Wilcox wrote: > On Mon, Apr 13, 2026 at 03:20:19PM -0400, Zi Yan wrote: >> collapse_file() requires FSes supporting large folio with at least >> PMD_ORDER, so replace the READ_ONLY_THP_FOR_FS check with that. >> MADV_COLLAPSE ignores shmem huge config, so exclude the check for shmem. >> >> While at it, replace VM_BUG_ON with VM_WARN_ON_ONCE. > > Why? These are bugs. I don't think we gain anything from continuing. The goal is to catch these issues during development. VM_BUG_ON crashes the system and that is too much for such issues in collapse_file(). > >> + /* >> + * skip files without PMD-order folio support >> + * do not check shmem, since MADV_COLLAPSE ignores shmem huge config >> + */ >> + if (!shmem_file(file) && mapping_max_folio_order(mapping) < PMD_ORDER) >> + return SCAN_FAIL; > > I wonder if it should. If the commit message to 5a90c155defa is > to be believed, > > Since 'deny' is for emergencies and 'force' is for testing, performance > issues should not be a problem in real production environments, so don't > call mapping_set_large_folios() in __shmem_get_inode() when large folio is > disabled with mount huge=never option (default policy). > > so maybe MADV_COLLAPSE should honour huge=never? > Documentation/filesystems/tmpfs.rst implies that we do! > > huge=never Do not allocate huge pages. This is the default. > huge=always Attempt to allocate huge page every time a new page is needed. > huge=within_size Only allocate huge page if it will be fully within i_size. > Also respect madvise(2) hints. > huge=advise Only allocate huge page if requested with madvise(2). > > so what's the difference between huge=never and huge=madvise? I think madvise means MADV_HUGEPAGE for the region, not MADV_COLLAPSE. In v1, I did the check for shmem, but that regressed MADV_COLLAPSE, which always can collapse THPs on shmem. I know it sounds unreasonable, but that ship has sailed. Best Regards, Yan, Zi