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n8gMquFWOdkYHWMFsXPYjTn2CIUa2ZqkFKclb7b7DYnhm5KV/35HRPWjd+KAmNle6MYLAIKIEJqo1TXMUKNF9MyrgWucrgji3kMOAhChlExh5pkf1iLeu8likm2xyvI7sZpBuFKbuFcxmBKRm7mxEBBQLHAKhqgyiYqwE6f3sLeQWdtC2jLomQOKeBUKo4tr1SF4kY9zhtaUDvgOZ6UJFHtmITUcvCIhCxeELiQ0kPrfyqpa9ZDmwYV+AHVA6hGPfgtHg44qQW8ry8mpqkq9fDQS7IgQjKsvHipxgcBR6iJY728alloPsdbopVJTwvlvMjiFncN+lYYb+pRleQVsaJankNCYOABxW44NwG36KfCgCPFU1epw1PGaqjQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000090, 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 19 Feb 2025, at 5:04, Baolin Wang wrote: > Hi Zi, > > Sorry for the late reply due to being busy with other things:) Thank you for taking a look at the patches. :) > > On 2025/2/19 07:54, Zi Yan wrote: >> During shmem_split_large_entry(), large swap entries are covering n slot= s >> and an order-0 folio needs to be inserted. >> >> Instead of splitting all n slots, only the 1 slot covered by the folio >> need to be split and the remaining n-1 shadow entries can be retained wi= th >> orders ranging from 0 to n-1. This method only requires >> (n/XA_CHUNK_SHIFT) new xa_nodes instead of (n % XA_CHUNK_SHIFT) * >> (n/XA_CHUNK_SHIFT) new xa_nodes, compared to the original >> xas_split_alloc() + xas_split() one. >> >> For example, to split an order-9 large swap entry (assuming XA_CHUNK_SHI= FT >> is 6), 1 xa_node is needed instead of 8. >> >> xas_try_split_min_order() is used to reduce the number of calls to >> xas_try_split() during split. > > For shmem swapin, if we cannot swap in the whole large folio by skipping = the swap cache, we will split the large swap entry stored in the shmem mapp= ing into order-0 swap entries, rather than splitting it into other orders o= f swap entries. This is because the next time we swap in a shmem folio thro= ugh shmem_swapin_cluster(), it will still be an order 0 folio. Right. But the swapin is one folio at a time, right? shmem_split_large_entr= y() should split the large swap entry and give you a slot to store the order-0 = folio. For example, with an order-9 large swap entry, to swap in first order-0 fol= io, the large swap entry will become order-0, order-0, order-1, order-2,=E2=80= =A6 order-8, after the split. Then the first order-0 swap entry can be used. Then, when a second order-0 is swapped in, the second order-0 can be used. When the last order-0 is swapped in, the order-8 would be split to order-7,order-6,=E2=80=A6,order-1,order-0, order-0, and the last order-0 wi= ll be used. Maybe the swapin assumes after shmem_split_large_entry(), all swap entries are order-0, which can lead to issues. There should be some check like if the swap entry order > folio_order, shmem_split_large_entry() should be used. > > Moreover I did a quick test with swapping in order 6 shmem folios, howeve= r, my test hung, and the console was continuously filled with the following= information. It seems there are some issues with shmem swapin handling. An= yway, I need more time to debug and test. To swap in order-6 folios, shmem_split_large_entry() does not allocate any new xa_node, since XA_CHUNK_SHIFT is 6. It is weird to see OOM error below. Let me know if there is anything I can help. > > [ 1037.364644] Huh VM_FAULT_OOM leaked out to the #PF handler. Retrying P= F > [ 1037.364650] Huh VM_FAULT_OOM leaked out to the #PF handler. Retrying P= F > [ 1037.364652] Huh VM_FAULT_OOM leaked out to the #PF handler. Retrying P= F > [ 1037.364654] Huh VM_FAULT_OOM leaked out to the #PF handler. Retrying P= F > [ 1037.364656] Huh VM_FAULT_OOM leaked out to the #PF handler. Retrying P= F > [ 1037.364658] Huh VM_FAULT_OOM leaked out to the #PF handler. Retrying P= F > [ 1037.364659] Huh VM_FAULT_OOM leaked out to the #PF handler. Retrying P= F > [ 1037.364661] Huh VM_FAULT_OOM leaked out to the #PF handler. Retrying P= F > [ 1037.364663] Huh VM_FAULT_OOM leaked out to the #PF handler. Retrying P= F > [ 1037.364665] Huh VM_FAULT_OOM leaked out to the #PF handler. Retrying P= F > [ 1042.368539] pagefault_out_of_memory: 9268696 callbacks suppressed > ....... Best Regards, Yan, Zi