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Date: Thu, 27 Aug 2020 02:55:28 -0700 From: Eric Dumazet <eric.dumazet@...il.com> To: "Li,Rongqing" <lirongqing@...du.com>, Eric Dumazet <eric.dumazet@...il.com>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org> Subject: Re: [PATCH] iavf: use kvzalloc instead of kzalloc for rx/tx_bi buffer On 8/27/20 1:53 AM, Li,Rongqing wrote: > > >> -----Original Message----- >> From: Eric Dumazet [mailto:eric.dumazet@...il.com] >> Sent: Thursday, August 27, 2020 4:26 PM >> To: Li,Rongqing <lirongqing@...du.com>; netdev@...r.kernel.org; >> intel-wired-lan@...ts.osuosl.org >> Subject: Re: [PATCH] iavf: use kvzalloc instead of kzalloc for rx/tx_bi buffer >> >> >> >> On 8/27/20 12:53 AM, Li RongQing wrote: >>> when changes the rx/tx ring to 4096, kzalloc may fail due to a >>> temporary shortage on slab entries. >>> >>> kvmalloc is used to allocate this memory as there is no need to have >>> this memory area physical continuously. >>> >>> Signed-off-by: Li RongQing <lirongqing@...du.com> >>> --- >> >> >> Well, fallback to vmalloc() overhead because order-1 pages are not readily >> available when the NIC is setup (usually one time per boot) is adding TLB cost >> at run time, for billions of packets to come, maybe for months. >> >> Surely trying a bit harder to get order-1 pages is desirable. >> >> __GFP_RETRY_MAYFAIL is supposed to help here. > > Could we add __GFP_RETRY_MAYFAIL to kvmalloc, to ensure the allocation success ? __GFP_RETRY_MAYFAIL does not _ensure_ the allocation success. The idea here is that for large allocations (bigger than PAGE_SIZE), kvmalloc_node() will not force __GFP_NORETRY, meaning that page allocator will not bailout immediately in case of memory pressure. This gives a chance for page reclaims to happen, and eventually the high order page allocation will succeed under normal circumstances. It is a trade-off, and only worth it for long living allocations.
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