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《Linux内存回收入口_nginux的博客-CSDN博客》前文我们概略的描述了几种内存回收入口#xff0c;我们知道几种回收入口最终都会调用进入shrink_node函数#xff0c;本文将以Linux 5.9源码来描述shrink_node函数的源码实现。
函数调用流程图 scan_control数据结构 str…概述
《Linux内存回收入口_nginux的博客-CSDN博客》前文我们概略的描述了几种内存回收入口我们知道几种回收入口最终都会调用进入shrink_node函数本文将以Linux 5.9源码来描述shrink_node函数的源码实现。
函数调用流程图 scan_control数据结构 struct scan_control {/* How many pages shrink_list() should reclaim */unsigned long nr_to_reclaim;/** Nodemask of nodes allowed by the caller. If NULL, all nodes* are scanned.*/nodemask_t *nodemask;/** The memory cgroup that hit its limit and as a result is the* primary target of this reclaim invocation.*/struct mem_cgroup *target_mem_cgroup;/** Scan pressure balancing between anon and file LRUs*/unsigned long anon_cost;unsigned long file_cost;/* Can active pages be deactivated as part of reclaim? *///是否能从active lru列表进行deactivate的reclaim
#define DEACTIVATE_ANON 1
#define DEACTIVATE_FILE 2unsigned int may_deactivate:2;//如果是1代表强制进行deactivate即同时deactivate file和anon//如果是0按需进行deactivate file或者anon具体条件见下面shrink_node源码分析unsigned int force_deactivate:1;unsigned int skipped_deactivate:1;/* Writepage batching in laptop mode; RECLAIM_WRITE */unsigned int may_writepage:1;/* Can mapped pages be reclaimed? */unsigned int may_unmap:1;/* Can pages be swapped as part of reclaim? */unsigned int may_swap:1;/** Cgroups are not reclaimed below their configured memory.low,* unless we threaten to OOM. If any cgroups are skipped due to* memory.low and nothing was reclaimed, go back for memory.low.*/unsigned int memcg_low_reclaim:1;unsigned int memcg_low_skipped:1;unsigned int hibernation_mode:1;/* One of the zones is ready for compaction */unsigned int compaction_ready:1;/* There is easily reclaimable cold cache in the current node *///设置为1代表只回收file page cache不回收aone pageunsigned int cache_trim_mode:1;/* The file pages on the current node are dangerously low *///设置1代表只回收aone page不回收file pageunsigned int file_is_tiny:1;/* Allocation order */s8 order;/* Scan (total_size priority) pages at once */s8 priority;/* The highest zone to isolate pages for reclaim from */s8 reclaim_idx;/* This contexts GFP mask */gfp_t gfp_mask;/* Incremented by the number of inactive pages that were scanned */unsigned long nr_scanned;/* Number of pages freed so far during a call to shrink_zones() */unsigned long nr_reclaimed;struct {unsigned int dirty;unsigned int unqueued_dirty;unsigned int congested;unsigned int writeback;unsigned int immediate;unsigned int file_taken;unsigned int taken;} nr;/* for recording the reclaimed slab by now */struct reclaim_state reclaim_state;
};
shrink_node函数 static void shrink_node(pg_data_t *pgdat, struct scan_control *sc)
{struct reclaim_state *reclaim_state current-reclaim_state;unsigned long nr_reclaimed, nr_scanned;struct lruvec *target_lruvec;bool reclaimable false;unsigned long file;target_lruvec mem_cgroup_lruvec(sc-target_mem_cgroup, pgdat);again:memset(sc-nr, 0, sizeof(sc-nr));nr_reclaimed sc-nr_reclaimed;nr_scanned sc-nr_scanned;/** Determine the scan balance between anon and file LRUs.*/spin_lock_irq(pgdat-lru_lock);sc-anon_cost target_lruvec-anon_cost;sc-file_cost target_lruvec-file_cost;spin_unlock_irq(pgdat-lru_lock);/** Target desirable inactive:active list ratios for the anon* and file LRU lists.*/if (!sc-force_deactivate) {unsigned long refaults;refaults lruvec_page_state(target_lruvec,WORKINGSET_ACTIVATE_ANON);//anon的refaults值比上次回收发生了变化或者inactive anon很少设置//DEACTIVATE_ANON表示需要deactivate anonif (refaults ! target_lruvec-refaults[0] ||inactive_is_low(target_lruvec, LRU_INACTIVE_ANON))sc-may_deactivate | DEACTIVATE_ANON;elsesc-may_deactivate ~DEACTIVATE_ANON;/** When refaults are being observed, it means a new* workingset is being established. Deactivate to get* rid of any stale active pages quickly.*/refaults lruvec_page_state(target_lruvec,WORKINGSET_ACTIVATE_FILE);if (refaults ! target_lruvec-refaults[1] ||inactive_is_low(target_lruvec, LRU_INACTIVE_FILE))sc-may_deactivate | DEACTIVATE_FILE;elsesc-may_deactivate ~DEACTIVATE_FILE;} elsesc-may_deactivate DEACTIVATE_ANON | DEACTIVATE_FILE;/** If we have plenty of inactive file pages that arent* thrashing, try to reclaim those first before touching* anonymous pages.*///file是inactive file的数量file lruvec_page_state(target_lruvec, NR_INACTIVE_FILE);if (file sc-priority !(sc-may_deactivate DEACTIVATE_FILE))//只回收file page影响get_scan_countsc-cache_trim_mode 1;elsesc-cache_trim_mode 0;/** Prevent the reclaimer from falling into the cache trap: as* cache pages start out inactive, every cache fault will tip* the scan balance towards the file LRU. And as the file LRU* shrinks, so does the window for rotation from references.* This means we have a runaway feedback loop where a tiny* thrashing file LRU becomes infinitely more attractive than* anon pages. Try to detect this based on file LRU size.*/if (!cgroup_reclaim(sc)) {unsigned long total_high_wmark 0;unsigned long free, anon;int z;free sum_zone_node_page_state(pgdat-node_id, NR_FREE_PAGES);file node_page_state(pgdat, NR_ACTIVE_FILE) node_page_state(pgdat, NR_INACTIVE_FILE);for (z 0; z MAX_NR_ZONES; z) {struct zone *zone pgdat-node_zones[z];if (!managed_zone(zone))continue;total_high_wmark high_wmark_pages(zone);}/** Consider anon: if thats low too, this isnt a* runaway file reclaim problem, but rather just* extreme pressure. Reclaim as per usual then.*/anon node_page_state(pgdat, NR_INACTIVE_ANON);//设置1代表只回收aone page不回收file pagesc-file_is_tiny file free total_high_wmark !(sc-may_deactivate DEACTIVATE_ANON) anon sc-priority;}//回收的核心函数后面文章专门分析shrink_node_memcgs(pgdat, sc);if (reclaim_state) {sc-nr_reclaimed reclaim_state-reclaimed_slab;reclaim_state-reclaimed_slab 0;}/* Record the subtrees reclaim efficiency */vmpressure(sc-gfp_mask, sc-target_mem_cgroup, true,sc-nr_scanned - nr_scanned,sc-nr_reclaimed - nr_reclaimed);//这一轮回收到了页面if (sc-nr_reclaimed - nr_reclaimed)reclaimable true;//只允许kswapd线程设置这些flag因为只有kswapd能clear这些flag避免混乱//比如memcg reclaim也能设置没法保证kswapd肯定会被wakeup去clear这些标志if (current_is_kswapd()) {/** If reclaim is isolating dirty pages under writeback,* it implies that the long-lived page allocation rate* is exceeding the page laundering rate. Either the* global limits are not being effective at throttling* processes due to the page distribution throughout* zones or there is heavy usage of a slow backing* device. The only option is to throttle from reclaim* context which is not ideal as there is no guarantee* the dirtying process is throttled in the same way* balance_dirty_pages() manages.** Once a node is flagged PGDAT_WRITEBACK, kswapd will* count the number of pages under pages flagged for* immediate reclaim and stall if any are encountered* in the nr_immediate check below.*///设置PGDAT_DIRTY代表reclaim发现很多页面正在回写if (sc-nr.writeback sc-nr.writeback sc-nr.taken)set_bit(PGDAT_WRITEBACK, pgdat-flags);/* Allow kswapd to start writing pages during reclaim.*/设置PGDAT_DIRTY代表reclaim发现很多脏页if (sc-nr.unqueued_dirty sc-nr.file_taken)set_bit(PGDAT_DIRTY, pgdat-flags);/** If kswapd scans pages marked for immediate* reclaim and under writeback (nr_immediate), it* implies that pages are cycling through the LRU* faster than they are written so also forcibly stall.*/if (sc-nr.immediate)congestion_wait(BLK_RW_ASYNC, HZ/10);}/** Tag a node/memcg as congested if all the dirty pages* scanned were backed by a congested BDI and* wait_iff_congested will stall.** Legacy memcg will stall in page writeback so avoid forcibly* stalling in wait_iff_congested().*///只允许kswapd线程设置LRUVEC_CONGESTED因为只有kswapd能clear LRUVEC_CONGESTED//比如memcg reclaim也能设置没法保证kswap能唤醒去clear LRUVEC_CONGESTED导致//direct reclaim阻塞在wait_iff_congestedif ((current_is_kswapd() ||(cgroup_reclaim(sc) writeback_throttling_sane(sc))) sc-nr.dirty sc-nr.dirty sc-nr.congested)set_bit(LRUVEC_CONGESTED, target_lruvec-flags);/** Stall direct reclaim for IO completions if underlying BDIs* and node is congested. Allow kswapd to continue until it* starts encountering unqueued dirty pages or cycling through* the LRU too quickly.*///如果是非kswapd线程且判定当前回收设置过拥塞flag就要等待所以direct reclaim//会被阻塞if (!current_is_kswapd() current_may_throttle() !sc-hibernation_mode test_bit(LRUVEC_CONGESTED, target_lruvec-flags))wait_iff_congested(BLK_RW_ASYNC, HZ/10);//如果需要继续回收就goto again继续if (should_continue_reclaim(pgdat, sc-nr_reclaimed - nr_reclaimed,sc))goto again;/** Kswapd gives up on balancing particular nodes after too* many failures to reclaim anything from them and goes to* sleep. On reclaim progress, reset the failure counter. A* successful direct reclaim run will revive a dormant kswapd.*/if (reclaimable)pgdat-kswapd_failures 0;
}
should_continue_reclaim /** Reclaim/compaction is used for high-order allocation requests. It reclaims* order-0 pages before compacting the zone. should_continue_reclaim() returns* true if more pages should be reclaimed such that when the page allocator* calls try_to_compact_pages() that it will have enough free pages to succeed.* It will give up earlier than that if there is difficulty reclaiming pages.*/
static inline bool should_continue_reclaim(struct pglist_data *pgdat,unsigned long nr_reclaimed,struct scan_control *sc)
{unsigned long pages_for_compaction;unsigned long inactive_lru_pages;int z;/* If not in reclaim/compaction mode, stop */if (!in_reclaim_compaction(sc))return false;/** Stop if we failed to reclaim any pages from the last SWAP_CLUSTER_MAX* number of pages that were scanned. This will return to the caller* with the risk reclaim/compaction and the resulting allocation attempt* fails. In the past we have tried harder for __GFP_RETRY_MAYFAIL* allocations through requiring that the full LRU list has been scanned* first, by assuming that zero delta of sc-nr_scanned means full LRU* scan, but that approximation was wrong, and there were corner cases* where always a non-zero amount of pages were scanned.*/if (!nr_reclaimed)return false;//compaction_suitable会检查水位是否已满足条件要根据orderPAGE_ALLOC_COSTLY_ORDER//使用不同的watermark,如果不满足就不会返回success/continue/* If compaction would go ahead or the allocation would succeed, stop */for (z 0; z sc-reclaim_idx; z) {struct zone *zone pgdat-node_zones[z];if (!managed_zone(zone))continue;//满足了水位return false代表不要继续shrink_node了switch (compaction_suitable(zone, sc-order, 0, sc-reclaim_idx)) {case COMPACT_SUCCESS:case COMPACT_CONTINUE:return false;default:/* check next zone */;}}/** If we have not reclaimed enough pages for compaction and the* inactive lists are large enough, continue reclaiming*///上面水位检查不通过且也没有reclaim足够的page来做compaction那就继续reclaim吧pages_for_compaction compact_gap(sc-order);inactive_lru_pages node_page_state(pgdat, NR_INACTIVE_FILE);if (get_nr_swap_pages() 0)inactive_lru_pages node_page_state(pgdat, NR_INACTIVE_ANON);return inactive_lru_pages pages_for_compaction;
} compaction_suitable会判定当前水位是否满足order申请如果满足了那么COMPACT_SUCCESS说明也不需要继续compact了如果不满了说明还没有回到足够order申请的内存逻辑会继续往下走到inactive_lru_pages pages_for_compaction逻辑判定如果inactive lru中有大于2被申请order的页面那就继续扫描回收
参考文章
[PATCH v2 4/4] mm/vmscan: Dont mess with pgdat-flags in memcg reclaim. - Andrey Ryabinin
Linux 内存管理_workingset内存_jianchwa的博客-CSDN博客
