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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1vNOBY-00000006RgQ-3Vfw; Mon, 24 Nov 2025 04:28:20 +0000 Date: Mon, 24 Nov 2025 04:28:20 +0000 From: Matthew Wilcox To: Harry Yoo Cc: Vlastimil Babka , Andrew Morton , Christoph Lameter , David Rientjes , Roman Gushchin , linux-mm@kvack.org Subject: Re: [PATCH v4 02/16] slab: Remove folio references from __ksize() Message-ID: References: <20251113000932.1589073-1-willy@infradead.org> <20251113000932.1589073-3-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam12 X-Rspam-User: X-Rspamd-Queue-Id: 4075414000A X-Stat-Signature: txowgmosrwtpfixgi1gt9c3wpz3qnu3h X-HE-Tag: 1763958507-740454 X-HE-Meta: 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 3Ijvt2V2 U27d6sYN8hbWVduDZkG4MkK0+4ljXweEqoBfBveGwjfA+nSdNLz8Y4ucy5ZYxw9xqeOYnw97LYgg73KHRzlUCJDZfsoWXIU38btRp+ROZt+bKkMxwLoHB9aVjdM/Bm8RfiU5sykFdILU39cougAgGmfbDjC7uBXxnMHxR7V9duBUX1H+eSwTUfLPOGeOvlm83EUTyxA7Z5zulNjTKd7DuQUrFSTgnPygEg0QsK2+r14rw46HsUxC3cucy0rXyzJZMdVUWAKFiiphpSQ+PBB6e7OZDNYU+ACVXWcgwgvJIU1T9DNc= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, 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, Nov 24, 2025 at 11:31:06AM +0900, Harry Yoo wrote: > > size_t __ksize(const void *object) > > { > > - struct folio *folio; > > + const struct page *page; > > + const struct slab *slab; > > > > if (unlikely(object == ZERO_SIZE_PTR)) > > return 0; > > > > - folio = virt_to_folio(object); > > + page = virt_to_page(object); > > > > - if (unlikely(!folio_test_slab(folio))) { > > - if (WARN_ON(folio_size(folio) <= KMALLOC_MAX_CACHE_SIZE)) > > - return 0; > > - if (WARN_ON(object != folio_address(folio))) > > - return 0; > > nit: we can still have these sanity checks even when we're not converting it > to folio? > > size_t size = large_kmalloc_size(page); > if (WARN_ON(size <= KMALLOC_MAX_CACHE_SIZE)) > return 0; > if (WARN_ON(object & (size - 1)) > return 0; > return size; We could! However, I decided that we had these extra warnings to catch some uses of ksize() on non-kmalloc-large objects, and so they were really caught by the new: + if (WARN_ON(!slab)) + return page_size(page); Now, you could argue that we're now not warning for ksize(kmalloc() + N) for N in the range 1..4095. But I'm not sure it's particularly useful to be warning for those cases. I suppose size <= KMALLOC_MAX_CACHE_SIZE would also catch an internal bug in kmalloc where we set PageLargeKmalloc on a small allocation, but given how few places actually call ksize(), I doubt this would be a useful self-check either.