Messages in this thread | | | Date | Mon, 9 Sep 2013 15:49:42 +0300 | From | Sergey Senozhatsky <> | Subject | Re: [PATCH 1/2] staging: zram: minimize `slot_free_lock' usage (v2) |
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> > Calling handle_pending_slot_free() for every RW operation may > > cause unneccessary slot_free_lock locking, because most likely > > process will see NULL slot_free_rq. handle_pending_slot_free() > > only when current detects that slot_free_rq is not NULL. > > > > v2: protect handle_pending_slot_free() with zram rw_lock. > > > > zram->slot_free_lock protects zram->slot_free_rq but shouldn't the zram > rw_lock be wrapped around the whole operation like the original code > does? I don't know the zram code, but the original looks like it makes > sense but in this one it looks like the locks are duplicative. > > Is the down_read() in the original code be changed to down_write()? >
I'm not touching locking around existing READ/WRITE commands.
the original code:
static void handle_pending_slot_free(struct zram *zram) { struct zram_slot_free *free_rq;
spin_lock(&zram->slot_free_lock); while (zram->slot_free_rq) { free_rq = zram->slot_free_rq; zram->slot_free_rq = free_rq->next; zram_free_page(zram, free_rq->index); kfree(free_rq); } spin_unlock(&zram->slot_free_lock); }
static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index, int offset, struct bio *bio, int rw) { int ret;
if (rw == READ) { down_read(&zram->lock); handle_pending_slot_free(zram); ret = zram_bvec_read(zram, bvec, index, offset, bio); up_read(&zram->lock); } else { down_write(&zram->lock); handle_pending_slot_free(zram); ret = zram_bvec_write(zram, bvec, index, offset); up_write(&zram->lock); }
return ret; }
the new one:
static void handle_pending_slot_free(struct zram *zram) { struct zram_slot_free *free_rq;
down_write(&zram->lock); spin_lock(&zram->slot_free_lock); while (zram->slot_free_rq) { free_rq = zram->slot_free_rq; zram->slot_free_rq = free_rq->next; zram_free_page(zram, free_rq->index); kfree(free_rq); } spin_unlock(&zram->slot_free_lock); up_write(&zram->lock); }
static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index, int offset, struct bio *bio, int rw) { int ret;
if (zram->slot_free_rq) handle_pending_slot_free(zram);
if (rw == READ) { down_read(&zram->lock); ret = zram_bvec_read(zram, bvec, index, offset, bio); up_read(&zram->lock); } else { down_write(&zram->lock); ret = zram_bvec_write(zram, bvec, index, offset); up_write(&zram->lock); }
return ret; }
both READ and WRITE operations are still protected by down_read() for READ path and down_write() for WRITE path. however, there is no handle_pending_slot_free() and zram->slot_free_lock locking on every READ/WRITE, instead handle_pending_slot_free() is called only when zram->slot_free_rq is not NULL. handle_pending_slot_free() in turn protects zram_free_page() call by down_write(), so no READ/WRITE operations are affected.
-ss
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