From 5e99893444a0e0582feb49d618195114b6e35760 Mon Sep 17 00:00:00 2001 From: Sergey Senozhatsky Date: Tue, 17 Sep 2024 11:09:12 +0900 Subject: zram: remove UNDER_WB and simplify writeback We now have only one active post-processing at any time, so we don't have same race conditions that we had before. If slot selected for post-processing gets freed or freed and reallocated it loses its PP_SLOT flag and there is no way for such a slot to gain PP_SLOT flag again until current post-processing terminates. Link: https://lkml.kernel.org/r/20240917021020.883356-8-senozhatsky@chromium.org Signed-off-by: Sergey Senozhatsky Cc: Minchan Kim Signed-off-by: Andrew Morton --- drivers/block/zram/zram_drv.c | 53 +++++++++++++------------------------------ drivers/block/zram/zram_drv.h | 1 - 2 files changed, 16 insertions(+), 38 deletions(-) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index c59a3e9218a9..263795c4aef7 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -390,10 +390,7 @@ static void mark_idle(struct zram *zram, ktime_t cutoff) for (index = 0; index < nr_pages; index++) { /* - * Do not mark ZRAM_UNDER_WB slot as ZRAM_IDLE to close race. - * See the comment in writeback_store. - * - * Also do not mark ZRAM_SAME slots as ZRAM_IDLE, because no + * Do not mark ZRAM_SAME slots as ZRAM_IDLE, because no * post-processing (recompress, writeback) happens to the * ZRAM_SAME slot. * @@ -402,7 +399,6 @@ static void mark_idle(struct zram *zram, ktime_t cutoff) zram_slot_lock(zram, index); if (!zram_allocated(zram, index) || zram_test_flag(zram, index, ZRAM_WB) || - zram_test_flag(zram, index, ZRAM_UNDER_WB) || zram_test_flag(zram, index, ZRAM_SAME)) { zram_slot_unlock(zram, index); continue; @@ -821,22 +817,17 @@ static ssize_t writeback_store(struct device *dev, index = pps->index; zram_slot_lock(zram, index); - if (!zram_test_flag(zram, index, ZRAM_PP_SLOT)) - goto next; /* - * Clearing ZRAM_UNDER_WB is duty of caller. - * IOW, zram_free_page never clear it. + * scan_slots() sets ZRAM_PP_SLOT and relases slot lock, so + * slots can change in the meantime. If slots are accessed or + * freed they lose ZRAM_PP_SLOT flag and hence we don't + * post-process them. */ - zram_set_flag(zram, index, ZRAM_UNDER_WB); - /* Need for hugepage writeback racing */ - zram_set_flag(zram, index, ZRAM_IDLE); + if (!zram_test_flag(zram, index, ZRAM_PP_SLOT)) + goto next; zram_slot_unlock(zram, index); - if (zram_read_page(zram, page, index, NULL)) { - zram_slot_lock(zram, index); - zram_clear_flag(zram, index, ZRAM_UNDER_WB); - zram_clear_flag(zram, index, ZRAM_IDLE); - zram_slot_unlock(zram, index); + if (zram_read_page(zram, page, index, NULL)) { release_pp_slot(zram, pps); continue; } @@ -852,11 +843,6 @@ static ssize_t writeback_store(struct device *dev, */ err = submit_bio_wait(&bio); if (err) { - zram_slot_lock(zram, index); - zram_clear_flag(zram, index, ZRAM_UNDER_WB); - zram_clear_flag(zram, index, ZRAM_IDLE); - zram_slot_unlock(zram, index); - release_pp_slot(zram, pps); /* * BIO errors are not fatal, we continue and simply @@ -871,25 +857,19 @@ static ssize_t writeback_store(struct device *dev, } atomic64_inc(&zram->stats.bd_writes); + zram_slot_lock(zram, index); /* - * We released zram_slot_lock so need to check if the slot was - * changed. If there is freeing for the slot, we can catch it - * easily by zram_allocated. - * A subtle case is the slot is freed/reallocated/marked as - * ZRAM_IDLE again. To close the race, idle_store doesn't - * mark ZRAM_IDLE once it found the slot was ZRAM_UNDER_WB. - * Thus, we could close the race by checking ZRAM_IDLE bit. + * Same as above, we release slot lock during writeback so + * slot can change under us: slot_free() or slot_free() and + * reallocation (zram_write_page()). In both cases slot loses + * ZRAM_PP_SLOT flag. No concurrent post-processing can set + * ZRAM_PP_SLOT on such slots until current post-processing + * finishes. */ - zram_slot_lock(zram, index); - if (!zram_allocated(zram, index) || - !zram_test_flag(zram, index, ZRAM_IDLE)) { - zram_clear_flag(zram, index, ZRAM_UNDER_WB); - zram_clear_flag(zram, index, ZRAM_IDLE); + if (!zram_test_flag(zram, index, ZRAM_PP_SLOT)) goto next; - } zram_free_page(zram, index); - zram_clear_flag(zram, index, ZRAM_UNDER_WB); zram_set_flag(zram, index, ZRAM_WB); zram_set_element(zram, index, blk_idx); blk_idx = 0; @@ -1538,7 +1518,6 @@ out: atomic64_dec(&zram->stats.pages_stored); zram_set_handle(zram, index, 0); zram_set_obj_size(zram, index, 0); - WARN_ON_ONCE(zram->table[index].flags & ~(1UL << ZRAM_UNDER_WB)); } /* diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h index 73a9d47d76ba..134be414e210 100644 --- a/drivers/block/zram/zram_drv.h +++ b/drivers/block/zram/zram_drv.h @@ -47,7 +47,6 @@ enum zram_pageflags { ZRAM_SAME = ZRAM_FLAG_SHIFT, /* Page consists the same element */ ZRAM_WB, /* page is stored on backing_device */ - ZRAM_UNDER_WB, /* page is under writeback */ ZRAM_PP_SLOT, /* Selected for post-processing */ ZRAM_HUGE, /* Incompressible page */ ZRAM_IDLE, /* not accessed page since last idle marking */ -- cgit v1.2.3