readahead: remove the old algorithm (c743d96b) · Commits · e / devices / android_kernel_xiaomi_markw

include/linux/fs.h

+1 −10

Original line number	Diff line number	Diff line
		@@ -701,14 +701,6 @@ struct fown_struct {
		* file_ra_state.la_index .ra_index .lookahead_index .readahead_index
		*/
		struct file_ra_state {
		unsigned long start; /* Current window */
		unsigned long size;
		unsigned long flags; /* ra flags RA_FLAG_xxx*/
		unsigned long cache_hit; /* cache hit count*/
		unsigned long prev_index; /* Cache last read() position */
		unsigned long ahead_start; /* Ahead window */
		unsigned long ahead_size;

		pgoff_t la_index; /* enqueue time */
		pgoff_t ra_index; /* begin offset */
		pgoff_t lookahead_index; /* time to do next readahead */
		@@ -717,10 +709,9 @@ struct file_ra_state {
		unsigned long ra_pages; /* Maximum readahead window */
		unsigned long mmap_hit; /* Cache hit stat for mmap accesses */
		unsigned long mmap_miss; /* Cache miss stat for mmap accesses */
		unsigned long prev_index; /* Cache last read() position */
		unsigned int prev_offset; /* Offset where last read() ended in a page */
		};
		#define RA_FLAG_MISS 0x01 /* a cache miss occured against this file */
		#define RA_FLAG_INCACHE 0x02 /* file is already in cache */

		/*
		* Measuring read-ahead sizes.

include/linux/mm.h

+0 −7

Original line number	Diff line number	Diff line
		@@ -1144,13 +1144,6 @@ unsigned long page_cache_readahead_ondemand(struct address_space *mapping,
		struct page *page,
		pgoff_t offset,
		unsigned long size);
		unsigned long page_cache_readahead(struct address_space *mapping,
		struct file_ra_state *ra,
		struct file *filp,
		pgoff_t offset,
		unsigned long size);
		void handle_ra_miss(struct address_space *mapping,
		struct file_ra_state *ra, pgoff_t offset);
		unsigned long max_sane_readahead(unsigned long nr);

		/* Do stack extension */

mm/readahead.c

+25 −348

Original line number	Diff line number	Diff line
		@@ -49,82 +49,6 @@ file_ra_state_init(struct file_ra_state ra, struct address_space mapping)
		}
		EXPORT_SYMBOL_GPL(file_ra_state_init);

		/*
		* Return max readahead size for this inode in number-of-pages.
		*/
		static inline unsigned long get_max_readahead(struct file_ra_state *ra)
		{
		return ra->ra_pages;
		}

		static inline unsigned long get_min_readahead(struct file_ra_state *ra)
		{
		return MIN_RA_PAGES;
		}

		static inline void reset_ahead_window(struct file_ra_state *ra)
		{
		/*
		* ... but preserve ahead_start + ahead_size value,
		* see 'recheck:' label in page_cache_readahead().
		* Note: We never use ->ahead_size as rvalue without
		* checking ->ahead_start != 0 first.
		*/
		ra->ahead_size += ra->ahead_start;
		ra->ahead_start = 0;
		}

		static inline void ra_off(struct file_ra_state *ra)
		{
		ra->start = 0;
		ra->flags = 0;
		ra->size = 0;
		reset_ahead_window(ra);
		return;
		}

		/*
		* Set the initial window size, round to next power of 2 and square
		* for small size, x 4 for medium, and x 2 for large
		* for 128k (32 page) max ra
		* 1-8 page = 32k initial, > 8 page = 128k initial
		*/
		static unsigned long get_init_ra_size(unsigned long size, unsigned long max)
		{
		unsigned long newsize = roundup_pow_of_two(size);

		if (newsize <= max / 32)
		newsize = newsize * 4;
		else if (newsize <= max / 4)
		newsize = newsize * 2;
		else
		newsize = max;
		return newsize;
		}

		/*
		* Set the new window size, this is called only when I/O is to be submitted,
		* not for each call to readahead. If a cache miss occured, reduce next I/O
		* size, else increase depending on how close to max we are.
		*/
		static inline unsigned long get_next_ra_size(struct file_ra_state *ra)
		{
		unsigned long max = get_max_readahead(ra);
		unsigned long min = get_min_readahead(ra);
		unsigned long cur = ra->size;
		unsigned long newsize;

		if (ra->flags & RA_FLAG_MISS) {
		ra->flags &= ~RA_FLAG_MISS;
		newsize = max((cur - 2), min);
		} else if (cur < max / 16) {
		newsize = 4 * cur;
		} else {
		newsize = 2 * cur;
		}
		return min(newsize, max);
		}

		#define list_to_page(head) (list_entry((head)->prev, struct page, lru))

		/**
		@@ -200,66 +124,6 @@ out:
		return ret;
		}

		/*
		* Readahead design.
		*
		* The fields in struct file_ra_state represent the most-recently-executed
		* readahead attempt:
		*
		* start: Page index at which we started the readahead
		* size: Number of pages in that read
		* Together, these form the "current window".
		* Together, start and size represent the `readahead window'.
		* prev_index: The page which the readahead algorithm most-recently inspected.
		* It is mainly used to detect sequential file reading.
		* If page_cache_readahead sees that it is again being called for
		* a page which it just looked at, it can return immediately without
		* making any state changes.
		* offset: Offset in the prev_index where the last read ended - used for
		* detection of sequential file reading.
		* ahead_start,
		* ahead_size: Together, these form the "ahead window".
		* ra_pages: The externally controlled max readahead for this fd.
		*
		* When readahead is in the off state (size == 0), readahead is disabled.
		* In this state, prev_index is used to detect the resumption of sequential I/O.
		*
		* The readahead code manages two windows - the "current" and the "ahead"
		* windows. The intent is that while the application is walking the pages
		* in the current window, I/O is underway on the ahead window. When the
		* current window is fully traversed, it is replaced by the ahead window
		* and the ahead window is invalidated. When this copying happens, the
		* new current window's pages are probably still locked. So
		* we submit a new batch of I/O immediately, creating a new ahead window.
		*
		* So:
		*
		* ----\|----------------\|----------------\|-----
		* ^start ^start+size
		* ^ahead_start ^ahead_start+ahead_size
		*
		* ^ When this page is read, we submit I/O for the
		* ahead window.
		*
		* A `readahead hit' occurs when a read request is made against a page which is
		* the next sequential page. Ahead window calculations are done only when it
		* is time to submit a new IO. The code ramps up the size agressively at first,
		* but slow down as it approaches max_readhead.
		*
		* Any seek/ramdom IO will result in readahead being turned off. It will resume
		* at the first sequential access.
		*
		* There is a special-case: if the first page which the application tries to
		* read happens to be the first page of the file, it is assumed that a linear
		* read is about to happen and the window is immediately set to the initial size
		* based on I/O request size and the max_readahead.
		*
		* This function is to be called for every read request, rather than when
		* it is time to perform readahead. It is called only once for the entire I/O
		* regardless of size unless readahead is unable to start enough I/O to satisfy
		* the request (I/O request > max_readahead).
		*/

		/*
		* do_page_cache_readahead actually reads a chunk of disk. It allocates all
		* the pages first, then submits them all for I/O. This avoids the very bad
		@@ -360,28 +224,6 @@ int force_page_cache_readahead(struct address_space mapping, struct file filp,
		return ret;
		}

		/*
		* Check how effective readahead is being. If the amount of started IO is
		* less than expected then the file is partly or fully in pagecache and
		* readahead isn't helping.
		*
		*/
		static inline int check_ra_success(struct file_ra_state *ra,
		unsigned long nr_to_read, unsigned long actual)
		{
		if (actual == 0) {
		ra->cache_hit += nr_to_read;
		if (ra->cache_hit >= VM_MAX_CACHE_HIT) {
		ra_off(ra);
		ra->flags \|= RA_FLAG_INCACHE;
		return 0;
		}
		} else {
		ra->cache_hit=0;
		}
		return 1;
		}

		/*
		* This version skips the IO if the queue is read-congested, and will tell the
		* block layer to abandon the readahead if request allocation would block.
		@@ -398,191 +240,6 @@ int do_page_cache_readahead(struct address_space mapping, struct file filp,
		return __do_page_cache_readahead(mapping, filp, offset, nr_to_read, 0);
		}

		/*
		* Read 'nr_to_read' pages starting at page 'offset'. If the flag 'block'
		* is set wait till the read completes. Otherwise attempt to read without
		* blocking.
		* Returns 1 meaning 'success' if read is successful without switching off
		* readahead mode. Otherwise return failure.
		*/
		static int
		blockable_page_cache_readahead(struct address_space mapping, struct file filp,
		pgoff_t offset, unsigned long nr_to_read,
		struct file_ra_state *ra, int block)
		{
		int actual;

		if (!block && bdi_read_congested(mapping->backing_dev_info))
		return 0;

		actual = __do_page_cache_readahead(mapping, filp, offset, nr_to_read, 0);

		return check_ra_success(ra, nr_to_read, actual);
		}

		static int make_ahead_window(struct address_space mapping, struct file filp,
		struct file_ra_state *ra, int force)
		{
		int block, ret;

		ra->ahead_size = get_next_ra_size(ra);
		ra->ahead_start = ra->start + ra->size;

		block = force \|\| (ra->prev_index >= ra->ahead_start);
		ret = blockable_page_cache_readahead(mapping, filp,
		ra->ahead_start, ra->ahead_size, ra, block);

		if (!ret && !force) {
		/* A read failure in blocking mode, implies pages are
		* all cached. So we can safely assume we have taken
		* care of all the pages requested in this call.
		* A read failure in non-blocking mode, implies we are
		* reading more pages than requested in this call. So
		* we safely assume we have taken care of all the pages
		* requested in this call.
		*
		* Just reset the ahead window in case we failed due to
		* congestion. The ahead window will any way be closed
		* in case we failed due to excessive page cache hits.
		*/
		reset_ahead_window(ra);
		}

		return ret;
		}

		/**
		* page_cache_readahead - generic adaptive readahead
		* @mapping: address_space which holds the pagecache and I/O vectors
		* @ra: file_ra_state which holds the readahead state
		* @filp: passed on to ->readpage() and ->readpages()
		* @offset: start offset into @mapping, in PAGE_CACHE_SIZE units
		* @req_size: hint: total size of the read which the caller is performing in
		* PAGE_CACHE_SIZE units
		*
		* page_cache_readahead() is the main function. It performs the adaptive
		* readahead window size management and submits the readahead I/O.
		*
		* Note that @filp is purely used for passing on to the ->readpage[s]()
		* handler: it may refer to a different file from @mapping (so we may not use
		* @filp->f_mapping or @filp->f_path.dentry->d_inode here).
		* Also, @ra may not be equal to &@filp->f_ra.
		*
		*/
		unsigned long
		page_cache_readahead(struct address_space mapping, struct file_ra_state ra,
		struct file *filp, pgoff_t offset, unsigned long req_size)
		{
		unsigned long max, newsize;
		int sequential;

		/*
		* We avoid doing extra work and bogusly perturbing the readahead
		* window expansion logic.
		*/
		if (offset == ra->prev_index && --req_size)
		++offset;

		/* Note that prev_index == -1 if it is a first read */
		sequential = (offset == ra->prev_index + 1);
		ra->prev_index = offset;
		ra->prev_offset = 0;

		max = get_max_readahead(ra);
		newsize = min(req_size, max);

		/* No readahead or sub-page sized read or file already in cache */
		if (newsize == 0 \|\| (ra->flags & RA_FLAG_INCACHE))
		goto out;

		ra->prev_index += newsize - 1;

		/*
		* Special case - first read at start of file. We'll assume it's
		* a whole-file read and grow the window fast. Or detect first
		* sequential access
		*/
		if (sequential && ra->size == 0) {
		ra->size = get_init_ra_size(newsize, max);
		ra->start = offset;
		if (!blockable_page_cache_readahead(mapping, filp, offset,
		ra->size, ra, 1))
		goto out;

		/*
		* If the request size is larger than our max readahead, we
		* at least want to be sure that we get 2 IOs in flight and
		* we know that we will definitly need the new I/O.
		* once we do this, subsequent calls should be able to overlap
		* IOs,* thus preventing stalls. so issue the ahead window
		* immediately.
		*/
		if (req_size >= max)
		make_ahead_window(mapping, filp, ra, 1);

		goto out;
		}

		/*
		* Now handle the random case:
		* partial page reads and first access were handled above,
		* so this must be the next page otherwise it is random
		*/
		if (!sequential) {
		ra_off(ra);
		blockable_page_cache_readahead(mapping, filp, offset,
		newsize, ra, 1);
		goto out;
		}

		/*
		* If we get here we are doing sequential IO and this was not the first
		* occurence (ie we have an existing window)
		*/
		if (ra->ahead_start == 0) { /* no ahead window yet */
		if (!make_ahead_window(mapping, filp, ra, 0))
		goto recheck;
		}

		/*
		* Already have an ahead window, check if we crossed into it.
		* If so, shift windows and issue a new ahead window.
		* Only return the #pages that are in the current window, so that
		* we get called back on the first page of the ahead window which
		* will allow us to submit more IO.
		*/
		if (ra->prev_index >= ra->ahead_start) {
		ra->start = ra->ahead_start;
		ra->size = ra->ahead_size;
		make_ahead_window(mapping, filp, ra, 0);
		recheck:
		/* prev_index shouldn't overrun the ahead window */
		ra->prev_index = min(ra->prev_index,
		ra->ahead_start + ra->ahead_size - 1);
		}

		out:
		return ra->prev_index + 1;
		}
		EXPORT_SYMBOL_GPL(page_cache_readahead);

		/*
		* handle_ra_miss() is called when it is known that a page which should have
		* been present in the pagecache (we just did some readahead there) was in fact
		* not found. This will happen if it was evicted by the VM (readahead
		* thrashing)
		*
		* Turn on the cache miss flag in the RA struct, this will cause the RA code
		* to reduce the RA size on the next read.
		*/
		void handle_ra_miss(struct address_space *mapping,
		struct file_ra_state *ra, pgoff_t offset)
		{
		ra->flags \|= RA_FLAG_MISS;
		ra->flags &= ~RA_FLAG_INCACHE;
		ra->cache_hit = 0;
		}

		/*
		* Given a desired number of PAGE_CACHE_SIZE readahead pages, return a
		* sensible upper limit.
		@@ -612,20 +269,40 @@ unsigned long ra_submit(struct file_ra_state *ra,
		}
		EXPORT_SYMBOL_GPL(ra_submit);

		/*
		* Set the initial window size, round to next power of 2 and square
		* for small size, x 4 for medium, and x 2 for large
		* for 128k (32 page) max ra
		* 1-8 page = 32k initial, > 8 page = 128k initial
		*/
		static unsigned long get_init_ra_size(unsigned long size, unsigned long max)
		{
		unsigned long newsize = roundup_pow_of_two(size);

		if (newsize <= max / 32)
		newsize = newsize * 4;
		else if (newsize <= max / 4)
		newsize = newsize * 2;
		else
		newsize = max;

		return newsize;
		}

		/*
		* Get the previous window size, ramp it up, and
		* return it as the new window size.
		*/
		static unsigned long get_next_ra_size2(struct file_ra_state *ra,
		static unsigned long get_next_ra_size(struct file_ra_state *ra,
		unsigned long max)
		{
		unsigned long cur = ra->readahead_index - ra->ra_index;
		unsigned long newsize;

		if (cur < max / 16)
		newsize = cur * 4;
		newsize = 4 * cur;
		else
		newsize = cur * 2;
		newsize = 2 * cur;

		return min(newsize, max);
		}
		@@ -701,7 +378,7 @@ ondemand_readahead(struct address_space *mapping,
		if (offset && (offset == ra->lookahead_index \|\|
		offset == ra->readahead_index)) {
		ra_index = ra->readahead_index;
		ra_size = get_next_ra_size2(ra, max);
		ra_size = get_next_ra_size(ra, max);
		la_size = ra_size;
		goto fill_ra;
		}