12 Matching Annotations
  1. Oct 2024
  2. elixir.bootlin.com elixir.bootlin.com
    page-writeback.c - mm/page-writeback.c - Linux source code v6.6.42 - Bootlin
    10
    1. YungTa.Chang 04 Oct 2024
      if (dtc->wb_thresh < 2 * wb_stat_error()) { wb_reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE); dtc->wb_dirty = wb_reclaimable + wb_stat_sum(wb, WB_WRITEBACK); } else { wb_reclaimable = wb_stat(wb, WB_RECLAIMABLE); dtc->wb_dirty = wb_reclaimable + wb_stat(wb, WB_WRITEBACK); }

      This is a configuration policy that does a more accurate calculation on the number of reclaimable pages and dirty pages when the threshold for the dirty pages in the writeback context is lower than 2 times the maximal error of a stat counter.

      #ldos #ldos-flag #ldos-policy-use #ldos-config
    2. YungTa.Chang 04 Oct 2024
      static long wb_min_pause(struct bdi_writeback *wb, long max_pause, unsigned long task_ratelimit, unsigned long dirty_ratelimit, int *nr_dirtied_pause

      This function is an algorithmic policy that determines the minimum throttle time for a process between consecutive writeback operations for dirty pages based on heuristics. It is used for balancing the load of the I/O subsystems so that there will not be excessive I/O operations that impact the performance of the system.

      #ldos #ldos-flag #ldos-policy-use #ldos-algo
    3. YungTa.Chang 04 Oct 2024
      if (!laptop_mode && nr_reclaimable > gdtc->bg_thresh && !writeback_in_progress(wb)) wb_start_background_writeback(wb);

      This is a configuration policy that determines whether to start background writeout. The code here indicates that if laptop_mode, which will reduce disk activity for power saving, is not set, then when the number of dirty pages reaches the bg_thresh threshold, the system starts writing back pages.

      #ldos #ldos-flag #ldos-policy-use #ldos-algo
    6. YungTa.Chang 03 Oct 2024
      if (dirty <= dirty_freerun_ceiling(thresh, bg_thresh) && (!mdtc || m_dirty <= dirty_freerun_ceiling(m_thresh, m_bg_thresh))) { unsigned long intv; unsigned long m_intv; free_running: intv = dirty_poll_interval(dirty, thresh); m_intv = ULONG_MAX; current->dirty_paused_when = now; current->nr_dirtied = 0; if (mdtc) m_intv = dirty_poll_interval(m_dirty, m_thresh); current->nr_dirtied_pause = min(intv, m_intv); break; } /* Start writeback even when in laptop mode */ if (unlikely(!writeback_in_progress(wb))) wb_start_background_writeback(wb); mem_cgroup_flush_foreign(wb); /* * Calculate global domain's pos_ratio and select the * global dtc by default. */ if (!strictlimit) { wb_dirty_limits(gdtc); if ((current->flags & PF_LOCAL_THROTTLE) && gdtc->wb_dirty < dirty_freerun_ceiling(gdtc->wb_thresh, gdtc->wb_bg_thresh)) /* * LOCAL_THROTTLE tasks must not be throttled * when below the per-wb freerun ceiling. */ goto free_running; } dirty_exceeded = (gdtc->wb_dirty > gdtc->wb_thresh) && ((gdtc->dirty > gdtc->thresh) || strictlimit); wb_position_ratio(gdtc); sdtc = gdtc; if (mdtc) { /* * If memcg domain is in effect, calculate its * pos_ratio. @wb should satisfy constraints from * both global and memcg domains. Choose the one * w/ lower pos_ratio. */ if (!strictlimit) { wb_dirty_limits(mdtc); if ((current->flags & PF_LOCAL_THROTTLE) && mdtc->wb_dirty < dirty_freerun_ceiling(mdtc->wb_thresh, mdtc->wb_bg_thresh)) /* * LOCAL_THROTTLE tasks must not be * throttled when below the per-wb * freerun ceiling. */ goto free_running; } dirty_exceeded |= (mdtc->wb_dirty > mdtc->wb_thresh) && ((mdtc->dirty > mdtc->thresh) || strictlimit); wb_position_ratio(mdtc); if (mdtc->pos_ratio < gdtc->pos_ratio) sdtc = mdtc; }

      This is an algorithmic policy that determines whether the process can run freely or a throttle is needed to control the rate of the writeback by checking if the number of dirty pages exceed the average of the global threshold and background threshold.

      #ldos #ldos-flag #ldos-policy-use #ldos-algo
    7. YungTa.Chang 03 Oct 2024
      shift = dirty_ratelimit / (2 * step + 1); if (shift < BITS_PER_LONG) step = DIV_ROUND_UP(step >> shift, 8); else step = 0; if (dirty_ratelimit < balanced_dirty_ratelimit) dirty_ratelimit += step; else dirty_ratelimit -= step;

      This is a configuration policy that determines how much we should increase/decrease the dirty_ratelimit, which controls the rate that processors write dirty pages back to storage.

      #ldos #ldos-flag #ldos-policy-use #ldos-config
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    elixir.bootlin.com/linux/v6.6.42/source/mm/page-writeback.c
  3. elixir.bootlin.com elixir.bootlin.com
    util.c - mm/util.c - Linux source code v6.6.42 - Bootlin
    2
    1. YungTa.Chang 03 Oct 2024
      if (sysctl_overcommit_kbytes) allowed = sysctl_overcommit_kbytes >> (PAGE_SHIFT - 10); else allowed = ((totalram_pages() - hugetlb_total_pages()) * sysctl_overcommit_ratio / 100); allowed += total_swap_pages;

      This is a configuration policy that specifies the amount of memory that the kernel will always be allowed to overcommit. If it is not set, then the amount of memories overcommitted will be proportional to the amount of pages available.

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    elixir.bootlin.com/linux/v6.6.42/source/mm/util.c