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linux-hyperv@vger.kernel.org; > akpm@linux-foundation.org; linux-mm@kvack.org > Cc: Dexuan Cui ; KY Srinivasan ; > Paul Rosswurm ; olaf@aepfle.de; vkuznets > ; davem@davemloft.net; wei.liu@kernel.org; Long Li > ; linux-kernel@vger.kernel.org; > linyunsheng@huawei.com; stable@vger.kernel.org; netdev@vger.kernel.org; > Alexander Duyck > Subject: [EXTERNAL] Re: [PATCH] mm: page_frag: Fix refill handling in > __page_frag_alloc_align() > > +cc netdev ML & Alexander > > On 3/1/2025 10:03 AM, Haiyang Zhang wrote: > > In commit 8218f62c9c9b ("mm: page_frag: use initial zero offset for > > page_frag_alloc_align()"), the check for fragsz is moved earlier. > > So when the cache is used up, and if the fragsz > PAGE_SIZE, it won't > > try to refill, and just return NULL. > > I tested it with fragsz:8192, cache-size:32768. After the initial four > > successful allocations, it failed, even there is plenty of free memory > > in the system. > > Hi, Haiyang > It seems the PAGE_SIZE is 4K for the tested system? Yes. > Which drivers or subsystems are passing the fragsz being bigger than > PAGE_SIZE to page_frag_alloc_align() related API? For example, our MANA driver when using jumbo frame. https://web.git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/tre= e/drivers/net/ethernet/microsoft/mana > > To fix, revert the refill logic like before: the refill is attempted > > before the check & return NULL. > > page_frag API is not really for allocating memory being bigger than > PAGE_SIZE as __page_frag_cache_refill() will not try hard enough to > allocate order 3 compound page when calling __alloc_pages() and will > fail back to allocate base page as the discussed in below: > https://lore.ker/ > nel.org%2Fall%2Fead00fb7-8538-45b3-8322- > 8a41386e7381%40huawei.com%2F&data=3D05%7C02%7Chaiyangz%40microsoft.com%7C= d73 > d6a0ae65b4a42681c08dd58c8087b%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%= 7 > C638764338396356411%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiO= i > IwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%= 7 > C&sdata=3DFJ7Ggrxxxv6QzKepUiHmtns1GZC2G2oJMcWSzOuFbsE%3D&reserved=3D0 We are already aware of this, and have error checking in place for the fail= over case to "base page". >From the discussion thread above, there are other drivers using page_frag_alloc_align() for over PAGE_SIZE too. If making the page_frag API support only fragsz <=3D PAGE_SIZE is desired, can we create another API? O= ne keeps the existing API semantics (allowing > PAGE_SIZE), the other uses your new code. By the way, it should add an explicit check and fail ALL req= uests for fragsz > PAGE_SIZE. Currently your code successfully allocates big frag= s for a few times, then fail. This is not a desired behavior. It's also a breaking change for our MANA driver, which can no longer run Jumbo frames. @Andrew Morton And other maintainers, could you please also evaluate the idea above? Thanks, - Haiyang