On 06/27/2017 12:09 AM, Paolo Valente wrote: > >> Il giorno 19 giu 2017, alle ore 13:43, Paolo Valente <paolo.valente@xxxxxxxxxx> ha scritto: >> >> This commit fixes a bug triggered by a non-trivial sequence of >> events. These events are briefly described in the next two >> paragraphs. The impatiens, or those who are familiar with queue >> merging and splitting, can jump directly to the last paragraph. >> >> On each I/O-request arrival for a shared bfq_queue, i.e., for a >> bfq_queue that is the result of the merge of two or more bfq_queues, >> BFQ checks whether the shared bfq_queue has become seeky (i.e., if too >> many random I/O requests have arrived for the bfq_queue; if the device >> is non rotational, then random requests must be also small for the >> bfq_queue to be tagged as seeky). If the shared bfq_queue is actually >> detected as seeky, then a split occurs: the bfq I/O context of the >> process that has issued the request is redirected from the shared >> bfq_queue to a new non-shared bfq_queue. As a degenerate case, if the >> shared bfq_queue actually happens to be shared only by one process >> (because of previous splits), then no new bfq_queue is created: the >> state of the shared bfq_queue is just changed from shared to non >> shared. >> >> Regardless of whether a brand new non-shared bfq_queue is created, or >> the pre-existing shared bfq_queue is just turned into a non-shared >> bfq_queue, several parameters of the non-shared bfq_queue are set >> (restored) to the original values they had when the bfq_queue >> associated with the bfq I/O context of the process (that has just >> issued an I/O request) was merged with the shared bfq_queue. One of >> these parameters is the weight-raising state. >> >> If, on the split of a shared bfq_queue, >> 1) a pre-existing shared bfq_queue is turned into a non-shared >> bfq_queue; >> 2) the previously shared bfq_queue happens to be busy; >> 3) the weight-raising state of the previously shared bfq_queue happens >> to change; >> the number of weight-raised busy queues changes. The field >> wr_busy_queues must then be updated accordingly, but such an update >> was missing. This commit adds the missing update. >> > > Hi Jens, > any idea of the possible fate of this fix? I sort of missed this one. It looks trivial enough for 4.12, or we can defer until 4.13. What do you think? -- Jens Axboe
