writeback, memcg: Implement cgroup_writeback_by_id()
Implement cgroup_writeback_by_id() which initiates cgroup writeback from bdi and memcg IDs. This will be used by memcg foreign inode flushing. v2: Use wb_get_lookup() instead of wb_get_create() to avoid creating spurious wbs. v3: Interpret 0 @nr as 1.25 * nr_dirty to implement best-effort flushing while avoding possible livelocks. Reviewed-by: Jan Kara <jack@suse.cz> Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <axboe@kernel.dk>
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@ -891,6 +891,89 @@ restart:
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wb_put(last_wb);
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}
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/**
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* cgroup_writeback_by_id - initiate cgroup writeback from bdi and memcg IDs
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* @bdi_id: target bdi id
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* @memcg_id: target memcg css id
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* @nr_pages: number of pages to write, 0 for best-effort dirty flushing
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* @reason: reason why some writeback work initiated
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* @done: target wb_completion
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*
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* Initiate flush of the bdi_writeback identified by @bdi_id and @memcg_id
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* with the specified parameters.
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*/
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int cgroup_writeback_by_id(u64 bdi_id, int memcg_id, unsigned long nr,
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enum wb_reason reason, struct wb_completion *done)
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{
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struct backing_dev_info *bdi;
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struct cgroup_subsys_state *memcg_css;
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struct bdi_writeback *wb;
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struct wb_writeback_work *work;
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int ret;
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/* lookup bdi and memcg */
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bdi = bdi_get_by_id(bdi_id);
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if (!bdi)
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return -ENOENT;
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rcu_read_lock();
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memcg_css = css_from_id(memcg_id, &memory_cgrp_subsys);
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if (memcg_css && !css_tryget(memcg_css))
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memcg_css = NULL;
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rcu_read_unlock();
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if (!memcg_css) {
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ret = -ENOENT;
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goto out_bdi_put;
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}
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/*
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* And find the associated wb. If the wb isn't there already
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* there's nothing to flush, don't create one.
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*/
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wb = wb_get_lookup(bdi, memcg_css);
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if (!wb) {
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ret = -ENOENT;
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goto out_css_put;
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}
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/*
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* If @nr is zero, the caller is attempting to write out most of
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* the currently dirty pages. Let's take the current dirty page
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* count and inflate it by 25% which should be large enough to
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* flush out most dirty pages while avoiding getting livelocked by
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* concurrent dirtiers.
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*/
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if (!nr) {
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unsigned long filepages, headroom, dirty, writeback;
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mem_cgroup_wb_stats(wb, &filepages, &headroom, &dirty,
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&writeback);
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nr = dirty * 10 / 8;
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}
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/* issue the writeback work */
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work = kzalloc(sizeof(*work), GFP_NOWAIT | __GFP_NOWARN);
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if (work) {
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work->nr_pages = nr;
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work->sync_mode = WB_SYNC_NONE;
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work->range_cyclic = 1;
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work->reason = reason;
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work->done = done;
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work->auto_free = 1;
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wb_queue_work(wb, work);
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ret = 0;
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} else {
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ret = -ENOMEM;
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}
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wb_put(wb);
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out_css_put:
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css_put(memcg_css);
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out_bdi_put:
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bdi_put(bdi);
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return ret;
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}
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/**
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* cgroup_writeback_umount - flush inode wb switches for umount
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*
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@ -217,6 +217,8 @@ void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
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void wbc_detach_inode(struct writeback_control *wbc);
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void wbc_account_cgroup_owner(struct writeback_control *wbc, struct page *page,
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size_t bytes);
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int cgroup_writeback_by_id(u64 bdi_id, int memcg_id, unsigned long nr_pages,
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enum wb_reason reason, struct wb_completion *done);
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void cgroup_writeback_umount(void);
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/**
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