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Thu, 23 Jan 2025 11:15:41 -0800 (PST) Message-ID: <2ef8b7d4-7fae-4a08-9db1-4a33cd56ec9c@broadcom.com> Date: Thu, 23 Jan 2025 11:15:39 -0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net-next v23 3/7] mm: page_frag: use initial zero offset for page_frag_alloc_align() To: Yunsheng Lin , davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com, Eric Dumazet Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Alexander Duyck , Andrew Morton , Linux-MM , Alexander Duyck References: <20241028115343.3405838-1-linyunsheng@huawei.com> <20241028115343.3405838-4-linyunsheng@huawei.com> Content-Language: en-US From: Florian Fainelli Autocrypt: addr=florian.fainelli@broadcom.com; keydata= xsBNBFPAG8ABCAC3EO02urEwipgbUNJ1r6oI2Vr/+uE389lSEShN2PmL3MVnzhViSAtrYxeT M0Txqn1tOWoIc4QUl6Ggqf5KP6FoRkCrgMMTnUAINsINYXK+3OLe7HjP10h2jDRX4Ajs4Ghs JrZOBru6rH0YrgAhr6O5gG7NE1jhly+EsOa2MpwOiXO4DE/YKZGuVe6Bh87WqmILs9KvnNrQ PcycQnYKTVpqE95d4M824M5cuRB6D1GrYovCsjA9uxo22kPdOoQRAu5gBBn3AdtALFyQj9DQ KQuc39/i/Kt6XLZ/RsBc6qLs+p+JnEuPJngTSfWvzGjpx0nkwCMi4yBb+xk7Hki4kEslABEB AAHNMEZsb3JpYW4gRmFpbmVsbGkgPGZsb3JpYW4uZmFpbmVsbGlAYnJvYWRjb20uY29tPsLB IQQQAQgAywUCZWl41AUJI+Jo+hcKAAG/SMv+fS3xUQWa0NryPuoRGjsA3SAUAAAAAAAWAAFr ZXktdXNhZ2UtbWFza0BwZ3AuY29tjDAUgAAAAAAgAAdwcmVmZXJyZWQtZW1haWwtZW5jb2Rp bmdAcGdwLmNvbXBncG1pbWUICwkIBwMCAQoFF4AAAAAZGGxkYXA6Ly9rZXlzLmJyb2FkY29t Lm5ldAUbAwAAAAMWAgEFHgEAAAAEFQgJChYhBNXZKpfnkVze1+R8aIExtcQpvGagAAoJEIEx tcQpvGagWPEH/2l0DNr9QkTwJUxOoP9wgHfmVhqc0ZlDsBFv91I3BbhGKI5UATbipKNqG13Z TsBrJHcrnCqnTRS+8n9/myOF0ng2A4YT0EJnayzHugXm+hrkO5O9UEPJ8a+0553VqyoFhHqA zjxj8fUu1px5cbb4R9G4UAySqyeLLeqnYLCKb4+GklGSBGsLMYvLmIDNYlkhMdnnzsSUAS61 WJYW6jjnzMwuKJ0ZHv7xZvSHyhIsFRiYiEs44kiYjbUUMcXor/uLEuTIazGrE3MahuGdjpT2 IOjoMiTsbMc0yfhHp6G/2E769oDXMVxCCbMVpA+LUtVIQEA+8Zr6mX0Yk4nDS7OiBlvOwE0E U8AbwQEIAKxr71oqe+0+MYCc7WafWEcpQHFUwvYLcdBoOnmJPxDwDRpvU5LhqSPvk/yJdh9k 4xUDQu3rm1qIW2I9Puk5n/Jz/lZsqGw8T13DKyu8eMcvaA/irm9lX9El27DPHy/0qsxmxVmU pu9y9S+BmaMb2CM9IuyxMWEl9ruWFS2jAWh/R8CrdnL6+zLk60R7XGzmSJqF09vYNlJ6Bdbs MWDXkYWWP5Ub1ZJGNJQ4qT7g8IN0qXxzLQsmz6tbgLMEHYBGx80bBF8AkdThd6SLhreCN7Uh IR/5NXGqotAZao2xlDpJLuOMQtoH9WVNuuxQQZHVd8if+yp6yRJ5DAmIUt5CCPcAEQEAAcLB gQQYAQIBKwUCU8AbwgUbDAAAAMBdIAQZAQgABgUCU8AbwQAKCRCTYAaomC8PVQ0VCACWk3n+ obFABEp5Rg6Qvspi9kWXcwCcfZV41OIYWhXMoc57ssjCand5noZi8bKg0bxw4qsg+9cNgZ3P N/DFWcNKcAT3Z2/4fTnJqdJS//YcEhlr8uGs+ZWFcqAPbteFCM4dGDRruo69IrHfyyQGx16s CcFlrN8vD066RKevFepb/ml7eYEdN5SRALyEdQMKeCSf3mectdoECEqdF/MWpfWIYQ1hEfdm C2Kztm+h3Nkt9ZQLqc3wsPJZmbD9T0c9Rphfypgw/SfTf2/CHoYVkKqwUIzI59itl5Lze+R5 wDByhWHx2Ud2R7SudmT9XK1e0x7W7a5z11Q6vrzuED5nQvkhAAoJEIExtcQpvGagugcIAJd5 EYe6KM6Y6RvI6TvHp+QgbU5dxvjqSiSvam0Ms3QrLidCtantcGT2Wz/2PlbZqkoJxMQc40rb fXa4xQSvJYj0GWpadrDJUvUu3LEsunDCxdWrmbmwGRKqZraV2oG7YEddmDqOe0Xm/NxeSobc MIlnaE6V0U8f5zNHB7Y46yJjjYT/Ds1TJo3pvwevDWPvv6rdBeV07D9s43frUS6xYd1uFxHC 7dZYWJjZmyUf5evr1W1gCgwLXG0PEi9n3qmz1lelQ8lSocmvxBKtMbX/OKhAfuP/iIwnTsww 95A2SaPiQZA51NywV8OFgsN0ITl2PlZ4Tp9hHERDe6nQCsNI/Us= In-Reply-To: <20241028115343.3405838-4-linyunsheng@huawei.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 379B840015 X-Stat-Signature: 54omqxa6gpg55enza34nweyd7esie1z5 X-Rspam-User: X-HE-Tag: 1737659743-184500 X-HE-Meta: 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 YrE+Q08w 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 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: Hi Yunsheng, On 10/28/24 04:53, Yunsheng Lin wrote: > We are about to use page_frag_alloc_*() API to not just > allocate memory for skb->data, but also use them to do > the memory allocation for skb frag too. Currently the > implementation of page_frag in mm subsystem is running > the offset as a countdown rather than count-up value, > there may have several advantages to that as mentioned > in [1], but it may have some disadvantages, for example, > it may disable skb frag coalescing and more correct cache > prefetching > > We have a trade-off to make in order to have a unified > implementation and API for page_frag, so use a initial zero > offset in this patch, and the following patch will try to > make some optimization to avoid the disadvantages as much > as possible. > > 1. https://lore.kernel.org/all/f4abe71b3439b39d17a6fb2d410180f367cadf5c.camel@gmail.com/ > > CC: Alexander Duyck > CC: Andrew Morton > CC: Linux-MM > Signed-off-by: Yunsheng Lin > Reviewed-by: Alexander Duyck Sorry for the late feedback, this patch causes the bgmac driver in is .ndo_open() function to return -ENOMEM, the call trace looks like this: bgmac_open -> bgmac_dma_init -> bgmac_dma_rx_skb_for_slot -> netdev_alloc_frag BGMAC_RX_ALLOC_SIZE = 10048 and PAGE_FRAG_CACHE_MAX_SIZE = 32768. Eventually we land into __page_frag_alloc_align() with the following parameters across multiple successive calls: __page_frag_alloc_align: fragsz=10048, align_mask=-1, size=32768, offset=0 __page_frag_alloc_align: fragsz=10048, align_mask=-1, size=32768, offset=10048 __page_frag_alloc_align: fragsz=10048, align_mask=-1, size=32768, offset=20096 __page_frag_alloc_align: fragsz=10048, align_mask=-1, size=32768, offset=30144 So in that case we do indeed have offset + fragsz (40192) > size (32768) and so we would eventually return NULL. Any idea on how to best fix that within the bgmac driver? Thanks! > --- > mm/page_frag_cache.c | 46 ++++++++++++++++++++++---------------------- > 1 file changed, 23 insertions(+), 23 deletions(-) > > diff --git a/mm/page_frag_cache.c b/mm/page_frag_cache.c > index 609a485cd02a..4c8e04379cb3 100644 > --- a/mm/page_frag_cache.c > +++ b/mm/page_frag_cache.c > @@ -63,9 +63,13 @@ void *__page_frag_alloc_align(struct page_frag_cache *nc, > unsigned int fragsz, gfp_t gfp_mask, > unsigned int align_mask) > { > +#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE) > + unsigned int size = nc->size; > +#else > unsigned int size = PAGE_SIZE; > +#endif > + unsigned int offset; > struct page *page; > - int offset; > > if (unlikely(!nc->va)) { > refill: > @@ -85,11 +89,24 @@ void *__page_frag_alloc_align(struct page_frag_cache *nc, > /* reset page count bias and offset to start of new frag */ > nc->pfmemalloc = page_is_pfmemalloc(page); > nc->pagecnt_bias = PAGE_FRAG_CACHE_MAX_SIZE + 1; > - nc->offset = size; > + nc->offset = 0; > } > > - offset = nc->offset - fragsz; > - if (unlikely(offset < 0)) { > + offset = __ALIGN_KERNEL_MASK(nc->offset, ~align_mask); > + if (unlikely(offset + fragsz > size)) { > + if (unlikely(fragsz > PAGE_SIZE)) { > + /* > + * The caller is trying to allocate a fragment > + * with fragsz > PAGE_SIZE but the cache isn't big > + * enough to satisfy the request, this may > + * happen in low memory conditions. > + * We don't release the cache page because > + * it could make memory pressure worse > + * so we simply return NULL here. > + */ > + return NULL; > + } > + > page = virt_to_page(nc->va); > > if (!page_ref_sub_and_test(page, nc->pagecnt_bias)) > @@ -100,33 +117,16 @@ void *__page_frag_alloc_align(struct page_frag_cache *nc, > goto refill; > } > > -#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE) > - /* if size can vary use size else just use PAGE_SIZE */ > - size = nc->size; > -#endif > /* OK, page count is 0, we can safely set it */ > set_page_count(page, PAGE_FRAG_CACHE_MAX_SIZE + 1); > > /* reset page count bias and offset to start of new frag */ > nc->pagecnt_bias = PAGE_FRAG_CACHE_MAX_SIZE + 1; > - offset = size - fragsz; > - if (unlikely(offset < 0)) { > - /* > - * The caller is trying to allocate a fragment > - * with fragsz > PAGE_SIZE but the cache isn't big > - * enough to satisfy the request, this may > - * happen in low memory conditions. > - * We don't release the cache page because > - * it could make memory pressure worse > - * so we simply return NULL here. > - */ > - return NULL; > - } > + offset = 0; > } > > nc->pagecnt_bias--; > - offset &= align_mask; > - nc->offset = offset; > + nc->offset = offset + fragsz; > > return nc->va + offset; > } -- Florian