+++ /dev/null
-// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
-// vim: ts=8 sw=2 smarttab
-
-#ifndef CEPH_READAHEAD_H
-#define CEPH_READAHEAD_H
-
-#include "Mutex.h"
-#include "Cond.h"
-#include <list>
-
-/**
- This class provides common state and logic for code that needs to perform readahead
- on linear things such as RBD images or files.
- Unless otherwise specified, all methods are thread-safe.
-
- Minimum and maximum readahead sizes may be violated by up to 50\% if alignment is enabled.
- Minimum readahead size may be violated if the end of the readahead target is reached.
- */
-class Readahead {
-public:
- typedef std::pair<uint64_t, uint64_t> extent_t;
-
- // equal to UINT64_MAX
- static const uint64_t NO_LIMIT = 18446744073709551615ULL;
-
- Readahead();
-
- ~Readahead();
-
- /**
- Update state with new reads and return readahead to be performed.
- If the length of the returned extent is 0, no readahead should be performed.
- The readahead extent is guaranteed not to pass \c limit.
-
- Note that passing in NO_LIMIT as the limit and truncating the returned extent
- is not the same as passing in the correct limit, because the internal state
- will differ in the two cases.
-
- @param extents read operations since last call to update
- @param limit size of the thing readahead is being applied to
- */
- extent_t update(const vector<extent_t>& extents, uint64_t limit);
-
- /**
- Update state with a new read and return readahead to be performed.
- If the length of the returned extent is 0, no readahead should be performed.
- The readahead extent is guaranteed not to pass \c limit.
-
- Note that passing in NO_LIMIT as the limit and truncating the returned extent
- is not the same as passing in the correct limit, because the internal state
- will differ in the two cases.
-
- @param offset offset of the read operation
- @param length length of the read operation
- @param limit size of the thing readahead is being applied to
- */
- extent_t update(uint64_t offset, uint64_t length, uint64_t limit);
-
- /**
- Increment the pending counter.
- */
- void inc_pending(int count = 1);
-
- /**
- Decrement the pending counter.
- The counter must not be decremented below 0.
- */
- void dec_pending(int count = 1);
-
- /**
- Waits until the pending count reaches 0.
- */
- void wait_for_pending();
- void wait_for_pending(Context *ctx);
-
- /**
- Sets the number of sequential requests necessary to trigger readahead.
- */
- void set_trigger_requests(int trigger_requests);
-
- /**
- Gets the minimum size of a readahead request, in bytes.
- */
- uint64_t get_min_readahead_size(void);
-
- /**
- Gets the maximum size of a readahead request, in bytes.
- */
- uint64_t get_max_readahead_size(void);
-
- /**
- Sets the minimum size of a readahead request, in bytes.
- */
- void set_min_readahead_size(uint64_t min_readahead_size);
-
- /**
- Sets the maximum size of a readahead request, in bytes.
- */
- void set_max_readahead_size(uint64_t max_readahead_size);
-
- /**
- Sets the alignment units.
- If the end point of a readahead request can be aligned to an alignment unit
- by increasing or decreasing the size of the request by 50\% or less, it will.
- Alignments are tested in order, so larger numbers should almost always come first.
- */
- void set_alignments(const std::vector<uint64_t> &alignments);
-
-private:
- /**
- Records that a read request has been received.
- m_lock must be held while calling.
- */
- void _observe_read(uint64_t offset, uint64_t length);
-
- /**
- Computes the next readahead request.
- m_lock must be held while calling.
- */
- extent_t _compute_readahead(uint64_t limit);
-
- /// Number of sequential requests necessary to trigger readahead
- int m_trigger_requests;
-
- /// Minimum size of a readahead request, in bytes
- uint64_t m_readahead_min_bytes;
-
- /// Maximum size of a readahead request, in bytes
- uint64_t m_readahead_max_bytes;
-
- /// Alignment units, in bytes
- std::vector<uint64_t> m_alignments;
-
- /// Held while reading/modifying any state except m_pending
- Mutex m_lock;
-
- /// Number of consecutive read requests in the current sequential stream
- int m_nr_consec_read;
-
- /// Number of bytes read in the current sequenial stream
- uint64_t m_consec_read_bytes;
-
- /// Position of the read stream
- uint64_t m_last_pos;
-
- /// Position of the readahead stream
- uint64_t m_readahead_pos;
-
- /// When readahead is already triggered and the read stream crosses this point, readahead is continued
- uint64_t m_readahead_trigger_pos;
-
- /// Size of the next readahead request (barring changes due to alignment, etc.)
- uint64_t m_readahead_size;
-
- /// Number of pending readahead requests, as determined by inc_pending() and dec_pending()
- int m_pending;
-
- /// Lock for m_pending
- Mutex m_pending_lock;
-
- /// Waiters for pending readahead
- std::list<Context *> m_pending_waiting;
-};
-
-#endif
Code Review / stor4nfv.git / blobdiff