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Message-Id: <20140814142225.50911fd0a0bf65427a1a214f@linux-foundation.org> Date: Thu, 14 Aug 2014 14:22:25 -0700 From: Andrew Morton <akpm@...ux-foundation.org> To: Gioh Kim <gioh.kim@....com> Cc: Alexander Viro <viro@...iv.linux.org.uk>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, Peter Zijlstra <peterz@...radead.org>, Jan Kara <jack@...e.cz>, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, "Theodore Ts'o" <tytso@....edu>, Andreas Dilger <adilger.kernel@...ger.ca>, linux-ext4@...r.kernel.org, Minchan Kim <minchan@...nel.org>, Joonsoo Kim <js1304@...il.com>, 이건호 <gunho.lee@....com> Subject: Re: [PATCH 1/2] fs/buffer.c: allocate buffer cache from non-movable area On Thu, 14 Aug 2014 14:15:40 +0900 Gioh Kim <gioh.kim@....com> wrote: > A buffer cache is allocated from movable area > because it is referred for a while and released soon. > But some filesystems are taking buffer cache for a long time > and it can disturb page migration. > > A new API should be introduced to allocate buffer cache from > non-movable area. I think the API could and should be more flexible than this. Rather than making the API be "movable or not movable", let's permit callers to specify the gfp_t and leave it at that. That way, if someone later wants to allocate a buffer head with, I dunno, __GFP_NOTRACK then they can do so. So the word "movable" shouldn't appear in buffer.c at all, except in a single place. > --- a/fs/buffer.c > +++ b/fs/buffer.c > @@ -993,7 +993,7 @@ init_page_buffers(struct page *page, struct block_device *bdev, > */ > static int > grow_dev_page(struct block_device *bdev, sector_t block, > - pgoff_t index, int size, int sizebits) > + pgoff_t index, int size, int sizebits, gfp_t movable_mask) s/movable_mask/gfp/ > { > struct inode *inode = bdev->bd_inode; > struct page *page; > @@ -1003,7 +1003,8 @@ grow_dev_page(struct block_device *bdev, sector_t block, > gfp_t gfp_mask; > > gfp_mask = mapping_gfp_mask(inode->i_mapping) & ~__GFP_FS; > - gfp_mask |= __GFP_MOVABLE; > + if (movable_mask & __GFP_MOVABLE) > + gfp_mask |= __GFP_MOVABLE; This becomes gfp_mask |= gfp; > /* > * XXX: __getblk_slow() can not really deal with failure and > * will endlessly loop on improvised global reclaim. Prefer > @@ -1058,7 +1059,8 @@ failed: > * that page was dirty, the buffers are set dirty also. > */ > static int > -grow_buffers(struct block_device *bdev, sector_t block, int size) > +grow_buffers(struct block_device *bdev, sector_t block, > + int size, gfp_t movable_mask) gfp > { > pgoff_t index; > int sizebits; > @@ -1085,11 +1087,12 @@ grow_buffers(struct block_device *bdev, sector_t block, int size) > } > > /* Create a page with the proper size buffers.. */ > - return grow_dev_page(bdev, block, index, size, sizebits); > + return grow_dev_page(bdev, block, index, size, sizebits, movable_mask); > } > > static struct buffer_head * > -__getblk_slow(struct block_device *bdev, sector_t block, int size) > +__getblk_slow(struct block_device *bdev, sector_t block, > + int size, gfp_t movable_mask) gfp > { > /* Size must be multiple of hard sectorsize */ > if (unlikely(size & (bdev_logical_block_size(bdev)-1) || > @@ -1111,7 +1114,7 @@ __getblk_slow(struct block_device *bdev, sector_t block, int size) > if (bh) > return bh; > > - ret = grow_buffers(bdev, block, size); > + ret = grow_buffers(bdev, block, size, movable_mask); gfp > if (ret < 0) > return NULL; > if (ret == 0) > @@ -1385,11 +1388,34 @@ __getblk(struct block_device *bdev, sector_t block, unsigned size) > > might_sleep(); > if (bh == NULL) > - bh = __getblk_slow(bdev, block, size); > + bh = __getblk_slow(bdev, block, size, __GFP_MOVABLE); Here is the place where buffer.c. mentions "movable". > return bh; > } > EXPORT_SYMBOL(__getblk); > > + /* > + * __getblk_nonmovable will locate (and, if necessary, create) the buffer_head > + * which corresponds to the passed block_device, block and size. The > + * returned buffer has its reference count incremented. > + * > + * The page cache is allocated from non-movable area > + * not to prevent page migration. > + * > + * __getblk()_nonmovable will lock up the machine > + * if grow_dev_page's try_to_free_buffers() attempt is failing. FIXME, perhaps? > + */ > +struct buffer_head * > +__getblk_nonmovable(struct block_device *bdev, sector_t block, unsigned size) > +{ > + struct buffer_head *bh = __find_get_block(bdev, block, size); > + > + might_sleep(); > + if (bh == NULL) > + bh = __getblk_slow(bdev, block, size, 0); > + return bh; > +} > +EXPORT_SYMBOL(__getblk_nonmovable); Suggest this be called __getblk_gfp(bdev, block, size, gfp) and then __getblk() be changed to call __getblk_gfp(..., __GFP_MOVABLE). We could then write a __getblk_nonmovable() which calls __getblk_gfp() (a static inlined one-line function) or we can just call __getblk_gfp(..., 0) directly from filesystems. > @@ -1423,6 +1450,28 @@ __bread(struct block_device *bdev, sector_t block, unsigned size) > } > EXPORT_SYMBOL(__bread); > > +/** > + * __bread_nonmovable() - reads a specified block and returns the bh > + * @bdev: the block_device to read from > + * @block: number of block > + * @size: size (in bytes) to read > + * > + * Reads a specified block, and returns buffer head that contains it. > + * The page cache is allocated from non-movable area > + * not to prevent page migration. > + * It returns NULL if the block was unreadable. > + */ > +struct buffer_head * > +__bread_nonmovable(struct block_device *bdev, sector_t block, unsigned size) > +{ > + struct buffer_head *bh = __getblk_slow(bdev, block, size, 0); > + > + if (likely(bh) && !buffer_uptodate(bh)) > + bh = __bread_slow(bh); > + return bh; > +} > +EXPORT_SYMBOL(__bread_nonmovable); Treat this in the same fashion as __getblk_nonmovable(). -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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